#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[top][i]);
        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--)
             print("%d", matrix[i][left]);
             left++;
        }
    }
    
    return 0;
    
}