#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll a, b, c; cin >> a >> b >> c;
  cout << (a*c + b*c - b*b - c*c) / (a - b) << endl;
}