#include<iostream>
using namespace std;
char a[100][100];
char s[100][100];

int main()
{
	
	int n,m;
	cin>>n>>m;
	int i,j,k,number,l;
	for(i = 0; i < m; ++i)
		for(j = 0; j < n; ++j)
			cin>>s[i][j];
		
	number = 0;
	for( i = 0; i < m; ++i)
	{
		number = 0;
		for(j = 0; j < n; ++j)
			for(k = j + 1; k < n; ++k)
				if(s[i][j] > s[i][k])
					number ++;	
				 j = 1;
				 l = 0;
		if(a[number][0] >= 'A' && a[number][0] <= 'Z')
		{
			while(a[number][j * n] >= 'A' && a[number][j * n] <= 'Z')
				j++;
			 l = j * n;
		}
		for(k = 0; k < n; ++k)
			a[number][l++] = s[i][k];
		
	}


	number = 0;
	for(i = 0; i < 100; ++i)
		for(j = 0; j < 100; ++j)
		{
			if(a[i][j] >='A' && a[i][j] <= 'Z')
			{
				cout<<a[i][j];
				++number;
				if(number == n)
				{
					cout<<endl;
					number = 0;
				}
			}
			else
				break;
			
		}
			return 0;
}