#include <bits/stdc++.h>   using namespace std;   long long a, b, w, x, c, ans;   int main() {     cin >> a >> b >> w >> x >> c;     if (c <= a) {       cout << 0 << endl;     } else {       ans = ceil(1.0 * (x * (c - a) - b) / (w - x));       cout << ans + c - a << endl;     }     return 0;   }   