#include <iostream>

using namespace std;

int main() {
	long long b1, b2, b3, b4;
	double r, d;
	cin >> b1 >> b2 >> b3;

	// r = 1.0 * (b3 - b2) / (b2 - b1);
	// d = b2 - r * b1;
	// cout << r << ", " << d << endl;
	// b4 = r * b3 + d;
	b4 = (b3 - b1) * (b3 - b2) / (b2 - b1) + b2;

	cout << b4 << endl;
	return 0;
}