include<bits/stdc++.h>

using namespace std; int main(){

double a,b,c;
cin>>a>>b>>c;
double p=(a+b+c)/2;
cout<<"area=";
cout<<setiosflags(ios::fixed)<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c))<<endl;
return 0;

}