#include <bits/stdc++.h>
int c, v0, v1, a, l;
int main() {
  scanf("%d%d%d%d%d", &c, &v0, &v1, &a, &l);
  int ct = v0, days = 1;
  while (ct < c) {
    ++days;
    ct += std::min(v1, v0 + a * (days - 1)) - l;
  }
  printf("%d\n", days);
  return 0;
}
