题意，在一个n*n的棋盘上放置一些马，使这些马不能互相攻击，问最多能放多少。

思路：从第一行每隔一个放置一个马即可，注意n=1和n=2的情况要特判.

#include<cstdio>

int main(){

    int n, m, t;

    scanf("%d", &t);

    for(int i = 1;i <= t;i ++){

        scanf("%d%d", &n, &m);

        printf("Case %d: ", i);

        if(n == 1 || m == 1){

            printf("%d\n", n*m);

            continue;

        }

        if(n == 2 || m == 2){

            if(m == 2) m = m^n, n = m^n, m=m^n;

            int tmp = m/4 * 4;

            if(m % 4 > 1) tmp += 4;

            else if(m % 4 == 1) tmp += 2;

            printf("%d\n", tmp);

            continue;

        }

        if(m & 1){

            if(n & 1) printf("%d\n", m*(n/2)+m/2+1);

            else printf("%d\n", m*n/2);

        }else {

            if(n & 1) printf("%d\n", m*(n/2)+m/2);

            else printf("%d\n", m*n/2);

        }

    }

    return 0;

}