多组数据好坑啊，王记清零了wa一次
#include <iostream>
#include <stdio.h>
using namespace std;

int row, column;
char pic[40][40];
bool used[26];
char zimu[26];
int zimuGs;
bool tu[26][26];
int rbGs[26];//入边的条数
int zimuIdx[26];
int stk[26];
int pxIdx[26];

bool visited[26];

void init(){
	for(int i = 0; i < 26; i++) used[i] = 0;
	for(int i = 0; i < 26; i++)
		for(int j = 0; j < 26; j++)
			tu[i][j] = 0;
	zimuGs = 0;
	for(int i = 0; i < 26; i++) rbGs[i] = 0;
	for(int i = 0; i < 26; i++) visited[i] = 0;
}

void dfs(int gs);

int main() {
	while(scanf("%d%d", &row, &column) > 0){
		if(row == -1 && column == -1) return 0;
		init();
		int minX[26], maxX[26], minY[26], maxY[26];
		for(int i = 0; i < row; i++){
			char s[64];
			scanf("%s", s);
			for(int j = 0; j < column; j++){
				pic[i][j] = s[j];
				if(s[j] != '.' && !used[s[j]-'A']){
					used[s[j]-'A'] = true;
					zimuIdx[s[j]-'A'] = zimuGs;
					zimu[zimuGs] = s[j];
					zimuGs ++;
				}
			}
		}
		int pos = 0;
		for(int i = 0; i < 26; i++){
			if(!used[i]) continue;
			pxIdx[pos] = zimuIdx[i];
			pos ++;
		}
		//cout << zimuGs << endl;
		for(int i = 0; i < zimuGs; i++){
			minX[i] = minY[i] = 2147483647;
			maxX[i] = maxY[i] = 0;
		}
		for(int i = 0; i < row; i++){
			for(int j = 0; j < column; j++){
				if(pic[i][j] == '.') continue;
				int zmIdx = zimuIdx[pic[i][j] - 'A'];
				if(i < minX[zmIdx]) minX[zmIdx] = i;
				if(i > maxX[zmIdx]) maxX[zmIdx] = i;
				if(j < minY[zmIdx]) minY[zmIdx] = j;
				if(j > maxY[zmIdx]) maxY[zmIdx] = j;
			}
		}
		//建圖
		for(int i = 0; i < zimuGs; i++){
			int x1 = minX[i], y1 = minY[i], x2 = maxX[i], y2 = maxY[i];
			for(int j = y1; j < y2; j++){
				if(pic[x1][j] != zimu[i] && pic[x1][j] != '.'){
					tu[i][zimuIdx[pic[x1][j]-'A']] = 1;
					//rbGs[zimuIdx[pic[x1][j]-'A']] ++;
				}
			}
			for(int j = x1; j < x2; j++){
				if(pic[j][y2] != zimu[i] && pic[j][y2] != '.'){
					tu[i][zimuIdx[pic[j][y2]-'A']] = 1;
					//rbGs[zimuIdx[pic[j][y2]-'A']] ++;
				}
			}
			for(int j = y2; j > y1; j--){
				if(pic[x2][j] != zimu[i] && pic[x2][j] != '.'){
					tu[i][zimuIdx[pic[x2][j]-'A']] = 1;
					//rbGs[zimuIdx[pic[x2][j]-'A']] ++;
				}
			}
			for(int j = x2; j > x1; j--){
				if(pic[j][y1] != zimu[i] && pic[j][y1] != '.'){
					tu[i][zimuIdx[pic[j][y1]-'A']] = 1;
					//rbGs[zimuIdx[pic[j][y1]-'A']] ++;
				}
			}
		}
		for(int i = 0; i < zimuGs; i++){
			for(int j = 0; j < zimuGs; j++){
				if(tu[i][j]) rbGs[j]++;
			}
		}
		/*
		for(int i = 0; i < zimuGs; i++) cout << zimu[i] << " "; cout << endl;
		for(int i = 0; i < zimuGs; i++){
			for(int j = 0; j < zimuGs; j++){
				cout << tu[i][j] << " ";
			}
			cout << endl;
		}
		for(int i = 0; i < zimuGs; i++) cout << rbGs[i] << " "; cout << endl;
	*/
		dfs(0);
	}
	return 0;
}


void dfs(int gs){
	if(gs == zimuGs){
		for(int i = 0; i < gs; i++){
			printf("%c", zimu[stk[i]]);
		}
		printf("\n");
		return;
	}
	for(int ii = 0; ii < zimuGs; ii++){
		int i = pxIdx[ii];
		if(visited[i] || rbGs[i] > 0) continue;
		visited[i] = true;
		stk[gs] = i;
		for(int j = 0; j < zimuGs; j++){
			if(tu[i][j]) rbGs[j] --;
		}
		dfs(gs+1);
		for(int j = 0; j < zimuGs; j++){
			if(tu[i][j]) rbGs[j] ++;
		}
		visited[i] = false;
	}
}