#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){	
double a;
double b;
double c;
double p=(a+b+c)/2;
cin>>a>>b>>c;
cout<<fixed<<setprecision(1)<<sqrt(p*(p-a)*(p-b)*(p-c));
return 0;
}