Knights in Chessboard

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
int main(){
    int n, t, i = 1, result, a, b;
    char str[500];

    scanf("%d", &t);

    while(t--){
        scanf("%d %d", &a, &b);
        if(a <= 2 || b <= 3){
            result = 0;
        } else if (a == 3 && (b == 4 || b == 5)){
            result = 4;
        } else if (a == 3 && b == 6){
            result = 5;
        } else {
            result = ceil((a * b * 1.0) / 2);
        }

        printf("Case %d: %d\n", i, result);

        i++;
    }

    return 0;
}