C＋＋小问题 应该填什么

#define M 3
#define N 4
#include<stdio.h>
main()
{ int a[M][N]={{3,8,9,10},{2,5,-3,5},{7,0,-1,4}}, total, i, j;
total=0;
for(i=0;i<M;i=i+M-1)
for(j=0;j<N; j++)
total=total+a[i][j];
for(j=0;j<N; j=j+N-1)
for(i=1;i<M-1;i++)
total=total＋________
printf("%d\n",total);
}

#define M 3
#define N 4
#include<stdio.h>
void main()
{
    int a[M][N] = { {3,8,9,10},{2,5,-3,5},{7,0,-1,4} }, total, i, j;
    total = 0;
    for (i = 0; i < M; i = i + M - 1)
        for (j = 0; j < N; j++)
            total = total + a[i][j];
    for (j = 0; j < N; j = j + N - 1)
        for (i = 1; i < M - 1; i++)
            total = total + a[i][j]; //划横线的部分应该填a[i][j]
            printf("%d\n", total);
}

就是a[j][i]