#include<iostream>#include<stdio.h>#include<algorithm>#include<string.h>#include<math.h>#include<map>#include<queue>#include<stack>#define ll long long#define oo 1000000000#define pi acos(-1)using namespace std;int w,h,move[4][2]={{0,1},{1,0},{0,-1},{-1,0}};char arc[105][105];bool ok(char c){ int y,x,yy,xx,i,j,k; for (y=1;y<=h;y++) for (x=1;x<=w;x++)if (arc[y][x]==c) goto A; A: ; if (y>h) return false; k=0; if (arc[move[k][0]+y][move[k][1]+x]!=c) k++; k%=4; j=y+move[k][0]; i=x+move[k][1]; while (x!=i || y!=j) { if (arc[j][i]!=c) return false; if (arc[move[k][0]+j][move[k][1]+i]!=c) { k++; if (k==2) { yy=j; xx=i; } } k%=4; j=j+move[k][0]; i=i+move[k][1]; } for (i=y+1;i<yy;i++) for (j=x+1;j<xx;j++)if (arc[i][j]!='.') return false; return true;}int main(){ int i,j; char c; while (~scanf("%d%d",&h,&w)) { if (!h && !w) break; for (i=0;i<=h+1;i++) arc[i][0]=arc[i][w+1]='?'; for (i=0;i<=w+1;i++) arc[0][i]=arc[h+1][i]='?'; for (i=1;i<=h;i++) scanf("%s",arc[i]+1); for (c='A';c<='Z';c++) if (ok(c)) printf("%c",c); printf("n"); } return 0;}
