#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;i<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;
}