#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ii = pair<int, int>;
const int MOD(1e9 + 7);
const int MAXN(1e5 + 11);
int n, first, z, a, l;
int main() {
  scanf("%d%d%d%d%d", &n, &first, &z, &a, &l);
  int ans = 0;
  for (int ptr = 0; ptr < n;) {
    if (ptr)
      ptr += max(0, first - l);
    else
      ptr += first;
    first += a;
    first = min(first, z);
    ++ans;
  }
  printf("%d\n", ans);
  return 0;
}
