#include <iostream>
#define int long long
using namespace std;

int b[3];

signed main() {
	cin >> b[0] >> b[1] >> b[2];
	cout << (b[2] * (b[0] + b[1]) - b[1] * b[1] - b[2] * b[2]) / (b[0] - b[1]) << endl;
}