//write a program to find the area ot the right angle triangle 
//#include<stdio.h>
//int main(){
//    int a,b,c;
//    scanf("%d%d",&a,&b);
//    c=(0.5*a*b);
//    printf("%d",c);
//}
#include<stdio.h>
int main (){
    int a,b,c;
    scanf("%d%d",&a,&b);
    c=(b*h/2);
    printf("%d",c)
}