Problem:
Score : 100 points

Problem Statement

In K-city, there are n streets running east-west, and m streets running north-south. Each street running east-west and each street running north-south cross each other. We will call the smallest area that is surrounded by four streets a block. How many blocks there are in K-city?

Constraints

2 ≤ n, m ≤ 100

Input

Input is given from Standard Input in the following format:

n m

Output

Print the number of blocks in K-city.

Sample Input 1

3 4

Sample Output 1

6

There are six blocks, as shown below:

Sample Input 2

2 2

Sample Output 2

1

There are one block, as shown below:

Solution in C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<math.h>
#define MAX 100000

int main()
{
        int N;
        int a[MAX];
        int i;
        int cnt_4;//4の倍数の数
        int cnt_2;//2の倍数の数（ただし、４の倍数は含まない）
        int thresh;

        scanf("%d", &N);

        for(i=0; i<N; i++)
        {
                scanf("%d", &a[i]);
        }

        cnt_4 = 0;
        cnt_2 = 0;
        for(i=0; i<N; i++)
        {
                if(a[i]%4==0)
                {
                        cnt_4++;
                }
                else if(a[i]%2==0)
                {
                        cnt_2++;
                }
        }

        thresh = floor(N/2);

        if(cnt_4 >= thresh)
        {
                printf("Yes\n");
        }
        else if(cnt_2/2+cnt_4 >= thresh)
        {
                printf("Yes\n");
        }
        else
        {
                printf("No\n");
        }

        //printf("thresh: %d\ncnt_4: %d\ncnt_2: %d\n", thresh, cnt_4, cnt_2);

        return 0;
}