#include <bits/stdc++.h>
using namespace std;
int main() {
    long long int a, b, c;
    cin>>a>>b>>c;
    double s=(a+b+c)/2.0;
    double area=sqrt(s*(s-a)*(s-b)*(s-c)); 
    //海龍公式：√s (s-a)(s-b)(s-c)
    long long int value=(long long int)(round(area*area)); //四捨五入
    cout<<value<<endl;
    return 0;
}