#include <bits/stdc++.h>
int main() {
  int pages, start, max, increase, reread;
  std::cin >> pages;
  std::cin >> start;
  std::cin >> max;
  std::cin >> increase;
  std::cin >> reread;
  int days = 0;
  int currentPage = reread;
  int currentSpeed = start - reread;
  do {
    currentPage += currentSpeed;
    currentSpeed += increase;
    if (currentSpeed > max - reread) currentSpeed = max - reread;
    days++;
  } while (currentPage < pages);
  std::cout << days;
}
