#include<iostream>
using namespace std;
const int MININT = -100000; // 0x80000000; // 最小整形值，以VC为准
const int MAXINT = 100000; //0x7fffffff; // 最大整形值，以VC为准
const int MAX = 50;
const int MAXL = 300; 
char bd[MAX][MAX]; // 棋盘状态
int line, row; // 棋盘的行数和列数
bool useds[MAXL]; // 辅助变量，表示该字母是否被使用
typedef struct
{
	// 字母矩形上下左右边界值
	int up, down, left, right;
}Border;
Border borders[MAXL]; // 某字母在棋盘的边界情况
char letters[MAX * MAX]; // 棋盘中所有字母
int letlen; // letters的长度
char answer[MAX * MAX]; // 题目所要答案
void readbd(); // 读取棋盘状态
void scanBorders(); // 读取各个字母在棋盘的边界情况
void scanLetters(); // 获取letters信息
void getAnswer(); // 获取答案

int main()
{
	while(cin >> line >> row)
	{
		readbd();
		scanBorders();
		scanLetters();
		getAnswer();
		cout << answer << endl;
	}
	return 0;
}
void readbd()
{
	for(int i = 0; i < line; i++)
		for(int j = 0; j < row; j++)
			cin >> bd[i][j];
	return ;
}
void scanBorders()
{
	int i, j;
	char ch;
	for(i = 0; i < MAXL; i++)
	{
		borders[i].up = borders[i].left = MAXINT;
		borders[i].down = borders[i].right = MININT;
	}
	for(i = 0; i < line; i++)
		for(j = 0; j < row; j++)
		{
			ch = bd[i][j];
			if(i < borders[ch].up) borders[ch].up = i;
			if(j < borders[ch].left) borders[ch].left = j;
			if(i > borders[ch].down) borders[ch].down = i;
			if(j > borders[ch].right) borders[ch].right = j;
		}
	return ;
}
void scanLetters()
{
	char ch;
	memset(useds, false, sizeof(useds));
	useds['.'] = true;
	letlen = 0;
	for(int i = 0; i < line; i++)
		for(int j = 0; j < row; j++)
		{
			ch = bd[i][j];
			if(!useds[ch]) 
			{
				useds[ch] = true;
				letters[letlen++] = ch;
			}
		}
	return ; 
}
bool findout(int ch)
{
	char bdch;
	int u = borders[ch].up, d = borders[ch].down;
	int l = borders[ch].left, r = borders[ch].right;
	int inow, jnow;
	inow = u;
	for(jnow = l; jnow <= r; jnow++)
	{
		bdch = bd[inow][jnow];
		if(bdch != ch && !useds[bdch]) return false;
	}
	inow = d;
	for(jnow = l; jnow <= r; jnow++)
	{
		bdch = bd[inow][jnow];
		if(bdch != ch && !useds[bdch]) return false;
	}
	jnow = l;
	for(inow = u; inow <= d; inow++)
	{
		bdch = bd[inow][jnow];
		if(bdch != ch && !useds[bdch]) return false;
	}
	jnow = r;
	for(inow = u; inow <= d; inow++)
	{
		bdch = bd[inow][jnow];
		if(bdch != ch && !useds[bdch]) return false;
	}
	return true;
}
void getAnswer()
{
	char ch;
	int stack[MAX * MAX];
	int stlen = 0;
	memset(useds, false, sizeof(useds));	
	for(int i = 0; i < letlen; i++)
		for(int j = 0; j < letlen; j++)
		{
			ch = letters[j];
			// cout << "try " << ch << endl; //t
			if(!useds[ch] && findout(ch))
			{
			//	cout << "findout " << ch << "!" << endl; //t
				useds[ch] = true;
				stack[stlen++] = ch;
			}
		}
	for(i = stlen - 1; i >= 0; i--)
		answer[stlen - 1 - i] = stack[i];
	answer[stlen] = '\0';
	return ;
}

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