#include <iostream>
#include <cstdio>
using namespace std;

int main() {
	long long int A,B,ans;
	cin>>A>>B;
	if(A==B){
		ans=2*A;
	}else{
		ans=(A*A-B*B)/(A-B);
	}
	cout<<ans<<endl;
	return 0;
}