#include <bits/stdc++.h>
using namespace std;
long long b1, b2, b3;
int main() {
	cin >> b1 >> b2 >> b3;
	cout << (b3 * (b1 - b2) + b2 * (b2 - b3) + b1 * (b1 - b2)) / (b2 - b3) << endl;
	return 0;
}