#include <iostream>
using namespace std;
int x[4]={1,0,-1,0},y[4]={0,1,0,-1};
char ans1=' ',ans2=' ';
int main()
{
	int n,m;
	char a[1001][1001];
	cin>>n>>m;
	for (int i=1;i<=n;i++)
		for (int j=1;j<=m;j++)
			cin>>a[i][j];
	for (int i=1;i<=n;i++)
	{
		for (int j=1;j<=m;j++)
		{
			if (a[i][j]=='#')
				continue;
			for (int k=0;k<4;k++)
			{
				int t1=x[k]+i,t2=y[k]+j;
				if (a[t1][t2]=='#')
					continue;
				if (a[i][j]>ans1||a[i][j]==ans1&&a[t1][t2]>ans2)
				{
					ans1=a[i][j];
					ans2=a[t1][t2];
				}
			}
		}
	}
	if (ans1==' ')
		for (int i=1;i<=n;i++)
			for (int j=1;j<=m;j++)
				if (a[i][j]!='#'&&ans1<a[i][j])
					ans1=a[i][j];
	if (ans1==ans2)
		cout<<ans1;
	else
		cout<<ans1<<ans2;
	return 0;
}