#include <bits/stdc++.h>
using namespace std;
int binsearch(int arr[], int n, int element) {
  int low = 0, high = n - 1;
  while (low <= high) {
    int mid = low + (high - low) / 2;
    if (arr[mid] == element)
      return mid;
    else if (arr[mid] < element)
      low = mid + 1;
    else
      high = mid - 1;
  }
  return -1;
}
void printArr(int arr[], int n) {
  for (int i = 0; i < n; i++) {
    cout << arr[i] << " ";
  }
  cout << "\n";
  return;
}
int modexp(int x, unsigned int y, int p) {
  int res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
void solve() {
  int c, v0, v1, a, l;
  cin >> c >> v0 >> v1 >> a >> l;
  int pages_read = 0, days = 0;
  while (pages_read < c) {
    days++;
    if (days == 1)
      pages_read += min(v0, v1);
    else
      pages_read += min((v0 + a * (days - 1) - l), v1 - l);
  }
  cout << days << endl;
  return;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  while (t) {
    solve();
    t--;
  }
  return 0;
}
