#include<bits/stdc++.h>
using namespace std;

int main(){
	cin.tie(0),ios::sync_with_stdio(false);
	int64_t b1,b2,b3; cin>>b1>>b2>>b3;
	cout<<(b3*b3+b2*b2-b2*b3-b1*b3)/(b2-b1)<<"\n"s;
}