#include <bits/stdc++.h>
using namespace std;
int main() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int cnt = 1, p = v0, rate = v0;
  while (p < c) {
    rate = min(v1, rate + a);
    p += rate - l;
    cnt++;
  }
  cout << cnt;
  return 0;
}
