#include <stdio.h>
int main() {
    int m,n;
    scanf("%d %d", &n, &m);
    if(m < 0 || n < 0) {
        printf("-1");
        return 0;
    }
int a[100][100];
for(int i = 0; i < n; j++){
    for(int j = 0; j < n; j++){
        scanf("%d", &a[i][j]);
    }
}
int top = 0, bottom = m - 1;
int left = 0,right = n-1;
while(top <= bottom && left <= right)
{
    for(int i = left; 1 <= right; i++)
       printf("%d", a[top][i]);
       top++;
    for(int i = top; i <= bottom; i++
       printf("%d", a[top][i]);
       right--;
    if(top <= bottom){
    for(int i =right;i >= left; i--)
        printf("%d", a[bottom][i]);
        bottom--;
}
    if(left <= right){
       for(int i = bottom; i >=top;i--)
       printtf("%d",a[i][left]);
       left++
    }
}
return 0;
}