#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)
#define all(a) (a).begin(),(a).end()

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    ll a, b, c;
    cin >> a >> b >> c;
    ll ans = c*(c - a) + b*(b - c);
    ans /= b - a;
    cout << ans << '\n';
}