求调

#include<bits/stdc++.h>
using namespace std;
long double a, b, c;
long long ans;
int main(){
	cin >> a >> b >> c;
	ans = (a + b + c) / 2;
	if(a + b >= c && a + c >= b && b + c >= a){
		cout << fixed << setprecision(2) << sqrt(ans * (ans-a) * (ans-b) * (ans-c));
	}
	return 0;
}