#include <iostream>
#include <cstdlib>
#include <cmath>
using namespace std;
int main(int argc, char *argv[])
{
    float b,y,embadon,em;
    cin>>b;
    cin>>y;
    embadon = b*y/2;
    em = abs(embadon);
    cout<<"to embadon einai:"<<em<<endl;
    
    



    system("PAUSE");
    return 0;
}