#include <bits/stdc++.h>
using namespace std;
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int c, v0, v1, a, l, v;
  cin >> c >> v0 >> v1 >> a >> l;
  int i = 0, r = 0, count = 0;
  while (c > 0) {
    if (v0 + i * a <= v1) {
      v = v0 + i * a;
    } else {
      v = v1;
    }
    count++;
    i++;
    if (count > 1) {
      r = v - l;
    } else {
      r = v;
    }
    c = c - r;
    v = v0;
  }
  cout << count << endl;
  return 0;
}
