#include<stdio.h>
int main()
{
    int a,b,sum,t;
    scanf("%d%d%d",&a,&b,&t);
    if(a%2==1)
        a=a-1;
    if(b%2==1)
        b=b-1;
    sum=a*0.5+b*0.5;
    printf("%d\n",sum);

    return 0;
}