#include <bits/stdc++.h>
using namespace std;
long long a, b, w, x, c;
long long ans;
void deal() {
  if (c <= a) {
    ans = 0;
    return;
  }
  long long pt = (1ll * a * w - 1ll * w * c + b) / (x - w);
  ans = pt;
  if (abs(1ll * pt * (x - w)) < abs(1ll * a * w - 1ll * w * c + b)) ans++;
  return;
}
int main() {
  while (~scanf("%I64d%I64d%I64d%I64d%I64d", &a, &b, &w, &x, &c)) {
    deal();
    printf("%I64d\n", ans);
  }
  return 0;
}
