#include <iostream>
#include <list>
#include <map>
#include <set>

using namespace std;

set<string> data;
set<string> visited;
map<char,list<string>> mapp;

void dfs(string s){
    if(visited.count(s) > 0) return;
    visited.insert(s);
    for(string S : mapp[s[0]]) dfs(S);
    for(string S : mapp[s[1]]) dfs(S);
}

int main()
{
    int N;
    while(cin >> N){
        visited.clear();
        data.clear();
        mapp.clear();

        for(int i=0; i<N; i++){
            string s;
            cin >> s;
            if(data.count(s) > 0) continue;
            data.insert(s);
            mapp[s[0]].push_back(s);
            mapp[s[1]].push_back(s);
        }

        dfs(*(data.begin()));

        cout << (visited.size() == data.size() ? "YES" : "NO") << endl;
    }
    return 0;
}