//1/((1/r1)+(1/r2))
#include <bits/stdc++.h>
using namespace std;

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