#include <bits/stdc++.h>
int main() {
  double a, b, w, x, c;
  scanf("%lf %lf %lf %lf %lf", &a, &b, &w, &x, &c);
  long long lb = (long long)(ceil(((a - c) * w + b) / (x - w)) + 0.001);
  printf("%I64d\n", ((lb) > (0) ? (lb) : (0)));
}
