CF820A Mister B and Book Reading

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 $ v_{0} $ 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 $ v_{0} $ pages, at second — $ v_{0}+a $ pages, at third — $ v_{0}+2a $ pages, and so on). But Mister B is just a human, so he physically wasn't able to read more than $ v_{1} $ 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 $ , $ v_{0} $ , $ v_{1} $ , $ a $ and $ l $ ( $ 1

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

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.