#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int c, a, m, d, l;
  cin >> c >> a >> m >> d >> l;
  int ans = 0;
  int read = a;
  while (c > 0) {
    ans++;
    c -= read;
    read += d;
    if (read > m) {
      read = m;
    }
    if (c <= 0) {
      break;
    }
    c += l;
  }
  cout << ans << endl;
}
