#include <iostream>
using namespace std;
typedef long long LL;
int main(int argc, char* argv[])
{
	int b1,b2,b3;
	int d;
	cin>>b1>>b2>>b3;
	LL b4=((b3-b2)*(b3-b2))/(b2-b1)+b3;
	cout<<b4<<endl;
	return 0;
}