#include <bits/stdc++.h>
using namespace std;
template <typename G>
inline void read(G &x) {
  x = 0;
  char c;
  while (!isdigit(c = getchar()))
    ;
  do {
    x = x * 10 + c - '0';
  } while (isdigit(c = getchar()));
}
template <typename G>
inline void write(G x) {
  if (x > 9) write(x / 10);
  putchar(x % 10 + '0');
}
template <class T>
inline T min(T a, T b, T c) {
  return min(a, min(b, c));
}
template <class T>
inline T min(T a, T b, T c, T d) {
  return min(a, min(b, c, d));
}
template <class T>
inline T max(T a, T b, T c) {
  return max(a, max(b, c));
}
template <class T>
inline T max(T a, T b, T c, T d) {
  return max(a, max(b, c, d));
}
const int MAXN = 1e5 * 5;
const int base = 1e9 + 7;
const int N = 5000;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int c, v1, v2, a, l;
  cin >> c >> v1 >> v2 >> a >> l;
  c -= v1;
  v1 += a;
  v1 = min(v1, v2);
  int ans = 1;
  while (c > 0) {
    ++ans;
    c += l;
    c -= v1;
    v1 += a;
    v1 = min(v1, v2);
  }
  cout << ans << '\n';
  return 0;
}
