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