#include <bits/stdc++.h>
using namespace std;
int main() {
  long long a, b, w, x, c;
  cin >> a >> b >> w >> x >> c;
  if (a >= c) {
    cout << 0 << "\n";
    return 0;
  }
  long long num = (c - a) * x - b, dem = w - x;
  if (num % dem == 0)
    cout << c - a + num / dem << "\n";
  else
    cout << c - a + num / dem + 1 << "\n";
  return 0;
}
