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