// editor2
#include<stdio.h>
int main()
{
    int m,n;
    scanf("%d %d",&m,&n);
    if(m<0 || n<0){
        printf("-1");
        return 0;
    }
    int matrix[m][n];
    for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
            scanf("%d", matrix[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",matrix[top][i]);
            top++;
        }
        for(int i=top;i<=bottom;i++){
            printf("%d",matrix[i][right]);
            right--;
        }
        if(top<=bottom){
            for(int i=right;i>=left;i--){
                printf("%d",matrix[bottom][i]);
                bottom--;
            }
        }
        if(left<=right){
            for(int i=bottom;i>=top;i--){
            printf("%d",matrix[i][left]);
            left++;
        }
    }
    return 0;
}
}