#include <bits/stdc++.h>
int main() {
  int c, vo, term, v1, a, l, ans = 1, sum;
  scanf("%d%d%d%d%d", &c, &vo, &v1, &a, &l);
  sum = vo;
  term = vo + a;
  while (sum < c) {
    if (term < v1) {
      sum = term + sum - l;
      term = term + a;
    } else
      sum = sum + v1 - l;
    ans++;
  }
  printf("%d\n", ans);
  return 0;
}
