#include<bits/stdc++.h> using namespace std;

double f(double a,double b,double c) { double p=0; p=(a+b+c)/2; p=sqrt(p*(p-a)(p-b)(p-c)); return p; } int main() { double a,b,c; cin>>a>>b>>c; cout<<fixed<<setprecision(2)<<f(a,b,c); return 0; }