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

int main(){ float r1,r2; cin>>r1>>r2; cout<<fixed<<setprecision(2)<<1/((1/r1)+(1/r2)); return 0; }

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

int main(){
	float r1,r2;
	cin>>r1>>r2;
	cout<<fixed<<setprecision(2)<<1/((1/r1)+(1/r2));
	return 0;
}