#include<iostream>#include<stdio.h>#include<string.h>#include<algorithm>#include<vector>#include<queue>#define Max(a,b) ((a)>(b)?(a):(b))#define Min(a,b) ((a)<(b)?(a):(b))#define Abs(a) ((a)>0?(a):(-(a)))#define llong long long intusing namespace std;const int N=35;const int inf=(1<<30);int n,m,w;char mat[N][N];int pos[N][4];int total;bool vis[N];int indgr[N];bool line[N][N];void addedge(int u,int v){if(!line[v][u]){line[v][u]=true;indgr[u]++;}}void findcover(int now){int left=pos[now][1];int top=pos[now][0];int right=pos[now][3];int buttom=pos[now][2];for(int i=top;i<=buttom;i++){if(mat[i][left]!=now+'A'-1)//this point cannot be '.'this char{addedge(mat[i][left]-'A'+1,now);}if(mat[i][right]!=now+'A'-1)//this point cannot be '.'this char{addedge(mat[i][right]-'A'+1,now);}}for(int j=left+1;j<=right-1;j++){if(mat[top][j]!=now+'A'-1)//this point cannot be '.'this char{addedge(mat[top][j]-'A'+1,now);}if(mat[buttom][j]!=now+'A'-1)//this point cannot be '.'this char{addedge(mat[buttom][j]-'A'+1,now);}}}void dfs(int now,int deep,char * s){s[deep]='A'-1+now;if(deep==total){printf("%sn",s+1);return;}vis[now]=true;for(int i=1;i<=total;i++){if(line[now][i]){indgr[i]--;}}for(int i=1;i<=total;i++){if(!indgr[i]&&!vis[i]){dfs(i,deep+1,s);}}for(int i=1;i<=total;i++){if(line[now][i]){indgr[i]++;}}vis[now]=false;}void solve(){memset(line,0,sizeof(line));memset(indgr,0,sizeof(indgr));memset(pos,0,sizeof(pos));total=0;for(int i=0;i<N;i++){pos[i][0]=n+2;pos[i][1]=m+2;pos[i][2]=0;pos[i][3]=0;}for(int i=1;i<=n;i++) for(int j=1;j<=m;j++) { int now =mat[i][j]-'A'+1; total=Max(now,total); if(now!='.') { pos[now][0]=Min(i,pos[now][0]); pos[now][1]=Min(j,pos[now][1]); pos[now][2]=Max(i,pos[now][2]); pos[now][3]=Max(j,pos[now][3]); } }for(int i=1;i<=total;i++){findcover(i);}char s[N];memset(s,0,sizeof(s));for(int i=1;i<=total;i++){if(!indgr[i]){dfs(i,1,s);}}}int main(){while(EOF!=scanf("%d%d",&n,&m)){memset(mat,0,sizeof(mat));for(int i=1;i<=n;i++){scanf("%s",mat[i]+1);}solve();}return 0;}
