OI-codes/Luogu/problem/B2015/B2015.cpp

#include <bits/stdc++.h>

using namespace std;

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