#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <cstdio>
#include <climits>
#include <cassert>
using namespace std;

ifstream fin("frame.txt");
#define cin fin

struct rect {
  int l, d, r, u;
  rect() {
    l = d = INT_MAX;
    r = u = INT_MIN;
  }
};

typedef vector<vector<char> > field;
typedef map<char, set<char> > graph;

void scan_x(int l, const int y, const int r,
            const char name, const field& p, graph& g)
{
  for(; l <= r; l++)
    if(p[y][l] != name)
      g[name].insert(p[y][l]);
}

void scan_y(const int x, int d, const int u,
            const char name, const field& p, graph& g)
{
  for(; d <= u; d++)
    if(p[d][x] != name)
      g[name].insert(p[d][x]);
}

int level = 0;
void rec(vector<string>& result, /*const*/graph& g)
{
  if(g.empty()) {
    result.push_back("");
    if(result.size() > 1000) abort();
  }
  
  for(graph::iterator it = g.begin();
      it != g.end();
      ++it) {
    bool minimum = true;
    for(char c = 'A'; c <= 'Z' && minimum; ++c)
      if(g.count(c) && g[c].count(it->first)) minimum = false;
    
    if(minimum) {
      //cout << "level " << level << ", selected " << it->first << endl;
      graph cg = g;
      cg.erase(it->first);
      
      int now = result.size();
      level++;
      rec(result, cg);
      --level;
      for(; now < result.size(); now++)
        result[now] = it->first + result[now];
    }
  }
}

void
solve(field& p)
{
  map<char, rect> area;
  
  for(int i = 0; i < p.size(); i++) {
    const vector<char>& v = p[i];
    for(int j = 0; j < v.size(); j++) {
      if(v[j] == '.') continue;
      rect& r = area[v[j]];
      r.l = min(j, r.l);
      r.r = max(j, r.r);
      r.d = min(i, r.d);
      r.u = max(i, r.u);
    }
  }
  
  graph g;
  for(map<char, rect>::const_iterator it = area.begin();
      it != area.end();
      ++it) {
    const char  name = it->first;
    const rect& r    = it->second;
    g[name];
    
    scan_x(r.l, r.d, r.r, name, p, g);
    scan_y(r.r, r.d, r.u, name, p, g);
    scan_x(r.l, r.u, r.r, name, p, g);
    scan_y(r.l, r.d, r.u, name, p, g);
  }
  
  vector<string> result;
  rec(result, g);
  sort(result.begin(), result.end());
  for(int i = 0; i < result.size(); i++)
    cout << result[i] << endl;
  cout << endl;
}

int main()
{
  if(!fin) return -1;
  
  int h, w;
  while(cin >> h >> w, h || w) {
    field prob(h, vector<char>(w, '.'));
    
    for(int i = 0; i < h; i++)
      for(int j = 0; j < w; j++)
        cin >> prob[i][j];
    
    solve(prob);
  }
  
  return 0;
}