문제

링크

풀이

#include <iomanip>
#include <iostream>
using namespace std;
 
void solve(void) {
  double r1, r2, r3; cin >> r1 >> r2 >> r3;
 
  cout << fixed << setprecision(7) << (r1*r2*r3) / (r1*r2 + r2*r3 + r3*r1);
}
 
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
 
  solve();
  return 0;
}