#include <bits/stdc++.h>
using namespace std;
const int INF = 99009000;
const long long MOD = 1000000007;
const int N = 100001;
int main() {
  {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  };
  long long a, b, w, x, c;
  cin >> a >> b >> w >> x >> c;
  long long A = a * w + b;
  long long B = w * c;
  long long dif = B - A;
  if (dif <= 0)
    cout << 0 << "\n";
  else
    cout << (dif + w - x - 1) / (w - x) << "\n";
}
