#include<iostream>
#include<vector>

using namespace std;

typedef long long ll;

int main() {


	ll B1, B2, B3;
	
	cin >> B1 >> B2 >> B3;

	ll B4 = (B3 * B3 - B2 * B3 + B2 * B2 - B1 * B3) / (B2 - B1);
	cout << B4 << endl;

	return 0;
}