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c++解題

2-5 E.背單字

一、題目

E.背單字
Problem ID: vocabulary
    某天中午，小 B 收到了一封來自日文老師的信，裡面寫著下次上課時要考 n 個單字。然而這是一所自由的學校，每個學生都可以自由決定自己想上課的時間。於是小 B 決定他要等到他背完所有單字之後再去上課考試。聰明的小 B 每天早上可以背 a 個單字，但是每天晚上小 B 會忘記 b 個單字（如果小 B 現在記得的單字不到 b，小 B 就會把全部的單字忘光）。請告訴小 B 要在幾天後的下午小 B 才能記著全部 n 個單字去考試，或是小 B 永遠背不完 n 個單字。

Input

測試資料只有一行，包含 3 個非負整數 n, a, b，其意義與題目敘述相同。

• 0 ≤ n, a, b ≤ 106

Output

請輸出一個數字，代表小 B 要在幾天後的下午去上課並參加考試，或輸出 -1 表示小 B 永遠無法背完 n 個單字。
 

Sample Input Output

 1

 5 3 1 2

2

 5 3 2

3
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未知: Array and string offset access syntax with curly braces is deprecated 在檔案中的第 /include/functions.encoding.php 列 40
未知: Array and string offset access syntax with curly braces is deprecated 在檔案中的第 /include/functions.encoding.php 列 40
未知: Array and string offset access syntax with curly braces is deprecated 在檔案中的第 /include/functions.encoding.php 列 73
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 505
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 119
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 505
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 119
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 119
未知: Function get_magic_quotes_gpc() is deprecated 在檔案中的第 /class/libraries/vendor/xoops/xmf/src/Request.php 列 119
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined variable: disabled 在檔案中的第 /modules/tad_book3/function.php 列 818
通知: Undefined index: bootstrap 在檔案中的第 /modules/tadtools/preloads/core.php 列 68
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資料庫語法
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0.004174 - update tad_book3_docs set `count` = `count`+1 where tbdsn='482'
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0.000175 - SELECT * FROM modules WHERE dirname = 'tadtools'
0.000219 - SELECT * FROM config WHERE (`conf_modid` = '4') ORDER BY conf_order ASC
0.000184 - select mid from modules where dirname='tad_book3'
0.000291 - desc `tad_book3_data_center` `sort`
0.000184 - select `col_sn`,`data_name`,`data_sort`, `data_value` from `tad_book3_data_center` where `mid`= '9' and `col_name`='video_tbdsn_date' and `col_sn`='482' order by `sort` , `data_sort`
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0.000210 - select conf_value from config where conf_name ='allow_register'
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0.000168 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='11' and status='1' order by position
0.000174 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='14' and status='1' order by position
0.000166 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='15' and status='1' order by position
0.000143 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='17' and status='1' order by position
0.000150 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='16' and status='1' order by position
0.000139 - select `menuid`, `itemname`, `itemurl`, `target`, `icon`, `link_cate_name`, `link_cate_sn`, `read_group` from tad_themes_menu where of_level='18' and status='1' order by position
0.000417 - select a.* from tad_themes_files_center as a left join tad_themes as b on a.col_sn=b.theme_id where a.`col_name`='slide' and b.`theme_name`='school2015'
0.000230 - SELECT * FROM modules WHERE dirname = 'tad_login'
0.000326 - SELECT * FROM config WHERE (`conf_modid` = '14') ORDER BY conf_order ASC
總計: 57
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額外資訊
包含檔案: 204 檔案
使用記憶體: 6952176 bytes
計時
XOOPS 使用 0.115 秒來載入。
XOOPS Boot 使用 0.025 秒來載入。
Module init 使用 0.007 秒來載入。
XOOPS output init 使用 0.034 秒來載入。
Module display 使用 0.024 秒來載入。
Page rendering 使用 0.024 秒來載入。