Codeforces820A Mister B and Book Reading 2017-06-28 09:38 67人阅读 评论(0) 收藏

A. Mister B and Book Reading

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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.

Input

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.

Output

Print one integer — the number of days Mister B needed to finish the book.

Examples

input

5 5 10 5 4

output

1

input

12 4 12 4 1

output

3

input

15 1 100 0 0

output

15

Note

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.

———————————————————————————————————

题目的意思是有人看书 第一天看v0页，每天比前一天多a页但不会超过v1页，每天会往

上一天看过的最后l页，问c页的书几天能看完

思路：模拟，防止到终点看回去可以先处理第一天，后门每天先退后进