#include <bits/stdc++.h>
#define REP(i, a, n) for(ll i = ((ll) a); i < ((ll) n); i++)
using namespace std;
typedef long long ll;

int main(void) {
    ll b[3];
    REP (i, 0, 3) cin >> b[i];
    ll ans = ((b[2]*b[2] - b[1]*b[2] + b[1]*b[1] - b[0]*b[2]))/(b[1] - b[0]);
    cout << ans << endl;
    return 0;
}