#include<iostream>

using namespace std;

float chuvi(int a, int b, int c) {

    return a + b + c;

}

float dientich(int a, int b, int c) {

    float p = chuvi(a, b, c) / 2.0;

    return sqrt(p*(p - a)*(p - b)*(p - c));

}

int main(){

    float a, b, c;

    cout << "Nhap canh a: ";

    cin >> a;

    cout << "Nhap canh b: ";

    cin >> b;

    cout << "Nhap canh c: ";

    cin >> c;

    if (a >= b + c || b >= a + c || c >= a + b)

        cout << "Ba canh vua nhap khong phai la canh cua tam giac";

    else {

        cout << "Chu vi cua tam giac la: "<<chuvi(a,b,c)<<endl;

        cout << "Dien tich cua tam giac la: " << dientich(a, b, c)<<endl;   

        }   

        system("pause");

        return 0;}

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

int main()
{
    long long a,b;
    cin>>a>>b;
    cout<<(a*b)/2;
    return 0;
}