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