#include <bits/stdc++.h>
using namespace std;
long long a[1000010], d[1000010];
long long b[100010], c[1010][1010];
long long mn = 1e18, mx = -1e18, ans, cnt, sm = 1, n, m, cur;
bool ok, okk, u[1000010], uu[310][310], uk[1000010];
char ck[510][510], ch[100010];
int dx[4] = {0, 1, 0, -1}, dy[4] = {-1, 0, 1, 0};
vector<long long> g[900010], an[100];
int main() {
  std::ios::sync_with_stdio(false);
  long long cc, v, vv, aa, l;
  cin >> cc >> v >> vv >> aa >> l;
  while (cc > 0) {
    long long k = v + aa * cnt;
    k = min(k, vv);
    cc -= k;
    cnt++;
    if (cc <= 0) {
      cout << cnt;
      return 0;
    }
    cc += l;
  }
  return 0;
}
