#include<stdio.h>
#include<string.h>

struct node{
    char x,y;
}str[10010];

int cnt,flag,visited[10010];

void DFS(int cur){
    if(flag || str[cur].y=='m'){
        flag=1;
        return ;
    }
    for(int i=0;i<cnt;i++)
        if(!visited[i] && str[cur].y==str[i].x){
            visited[i]=1;
            DFS(i);
            visited[i]=0;
        }
}

int main(){

    //freopen("input.txt","r",stdin);

    int len;
    char word[1010];
    while(scanf("%s",word)!=EOF){
        if(word[0]=='0'){
            printf("No.\n");
            continue;
        }
        len=strlen(word);
        cnt=0;
        str[cnt].x=word[0];
        str[cnt++].y=word[len-1];
        while(scanf("%s",word)){
            if(word[0]=='0')
                break;
            len=strlen(word);
            str[cnt].x=word[0];
            str[cnt++].y=word[len-1];
        }
        flag=0;
        for(int i=0;i<cnt;i++)
            if(str[i].x=='b'){
                memset(visited,0,sizeof(visited));
                visited[i]=1;
                DFS(i);
            }
        if(flag)
            printf("Yes.\n");
        else
            printf("No.\n");
    }
    return 0;
}