#include <bits/stdc++.h>
using namespace std;
int main() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int n = 1;
  int x = 0;
  int t = 0;
  for (;;) {
    if (n == 1) {
      x = v0;
      t = v0;
      if (x >= c) {
        cout << 1 << endl;
        return 0;
      }
      n = 2;
    } else {
      x -= l;
      t += a;
      t = min(v1, t);
      x += t;
      if (x >= c) {
        cout << n << endl;
        return 0;
      }
      n++;
    }
  }
  return 0;
}
