Mister B and Book Reading
题目描述
Mister B once received a gift: it was a book about aliens, which he started read immediately. This book had c pages.
At first day Mister B read v0 pages, but after that he started to speed up. Every day, starting from the second, he read a pages more than on the previous day (at first day he read v0 pages, at second− v0+a pages, at third− v0+2a pages, and so on). But Mister B is just a human, so he physically wasn't able to read more than v1 pages per day.
Also, to refresh his memory, every day, starting from the second, Mister B had to reread last l pages he read on the previous day. Mister B finished the book when he read the last page for the first time.
Help Mister B to calculate how many days he needed to finish the book.
First and only line contains five space-separated integers: c, v0, v1, a and l (1≤c≤1000, 0≤l<v0≤v1≤1000, 0≤a≤1000) − the length of the book in pages, the initial reading speed, the maximum reading speed, the acceleration in reading speed and the number of pages for rereading.
Print one integer − the number of days Mister B needed to finish the book.
5 5 10 5 4
1
12 4 12 4 1
3
15 1 100 0 0
15
In the first sample test the book contains 5 pages, so Mister B read it right at the first day.
In the second sample test at first day Mister B read pages number 1-4, at second day− 4-11, at third day− 11-12 and finished the book.
In third sample test every day Mister B read 1 page of the book, so he finished in 15 days.
题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 130 题。保留原作者与原赛事署名。