#include <bits/stdc++.h>
using namespace std;
int main() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int speed = v0;
  int ans = 0;
  while (c > 0) {
    if (ans > 0)
      c = c - (speed) + l;
    else
      c = c - speed;
    speed = speed + a;
    if (speed > v1) speed = v1;
    ans++;
  }
  cout << ans;
  return 0;
}
