#include <bits/stdc++.h>
using namespace std;
int isprime(int n) {
  int i;
  for (i = 2; i * i <= n; i++) {
    if (n % i == 0) return 0;
  }
  return 1;
}
int main() {
  long long int n, k = 0, i = 0, m, x = 0, y, q, r, s, l, t, a, v0, v1, c, b,
                   j = 0, d = 0, ct = 0, sum = 0, h[1000009] = {0},
                   temp = 10000, fl = 0;
  cin >> c >> v0 >> v1 >> a >> l;
  for (i = 0;; i++) {
    if ((v0 + a * i) <= v1)
      c = c - (v0 + a * i);
    else
      c -= v1;
    if (c <= 0) break;
    c += l;
  }
  cout << i + 1;
}
