#include <stdio.h> #include <iso646.h> int main (void) {int A,B; double F=0.5; double C; scanf("%d%d",&A,&B); C=ABF; if (C>=0 and C<=5000) printf("%.1f",C); return 0; }

#include<stdio.h>
int main()
{
   int a,b;
   float c;
   scanf("%d%d",&a,&b);
   c=a*b*1.0/2;
   printf("%.1f",c);

    return 0;
}