B"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 xe2 x80 x89+ xe2 x80 x89a pages, at third -- v0 xe2 x80 x89+ xe2 x80 x892a 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 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89c xe2 x80 x89 xe2 x89 xa4 xe2 x80 x891000, 0 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89l xe2 x80 x89< xe2 x80 x89v0 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89v1 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x891000, 0 xe2 x80 x89 xe2 x89 xa4 xe2 x80 x89a xe2 x80 x89 xe2 x89 xa4 xe2 x80 x891000) -- 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. 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 xe2 x80 x89- xe2 x80 x894, at second day -- 4 xe2 x80 x89- xe2 x80 x8911, at third day -- 11 xe2 x80 x89- xe2 x80 x8912 and finished the book. In third sample test every day Mister B read 1 page of the book, so he finished in 15 days. "...