#include <bits/stdc++.h>
using namespace std;
double sqr(double a) { return a * a; }
struct point {
  int x, y;
};
int dll(int a) {
  for (int i = sqrt(a) + 1; i > 1; i--) {
    if (a % i == 0) {
      return i;
    }
  }
  return 1;
}
void prov(string s) {
  int k = 0, ot = 0;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == 'X') k++;
    if (s[i] == 'O') ot++;
  }
  if (k == 4 && !ot) {
    cout << "YES" << endl;
    exit(0);
  }
}
int main() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int ans = 1, now = v0;
  v0 = min(v0 + a, v1);
  while (now < c) {
    now += v0;
    now -= l;
    ans++;
    v0 = min(v0 + a, v1);
  }
  cout << ans;
  return 0;
}
