#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;i < mn; 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; 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 0;
}