;int mp[30][250][250];int main(){int n,u,v,i,j,l,k,p,f;char s[1024];while(~scanf(“%d”,&n)){if(n==0) break;memset(mp,0,sizeof(mp));while(~scanf(“%d%d”,&u,&v)){if(u==0&&v==0) break;scanf(“%s”,s);l=strlen(s);for(j=0; j<l; j++){mp[s[j]-‘a’][u][v]=1;}}for(p=0; p<26; p++){for(k=1; k<=n; k++)for(i=1; i<=n; i++){if(!mp[p][i][k]) continue;for(j=1; j<=n; j++){if(k==i||k==j||i==j) continue;if(mp[p][k][j])mp[p][i][j]=1;}}}while(~scanf(“%d%d”,&u,&v)){f=0;if(u==0&&v==0) break;for(i=0; i<26; i++){if(mp[i][u][v]){printf(“%c”,’a’+i);f=1;}}if(f==0) printf(“-“);printf(“\n”);}printf(“\n”);}return 0;}
，绊脚石乃是进身之阶。
