#include <bits/stdc++.h>

using namespace std;

typedef long long int ll;
typedef long double ld;

typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<ii> vii;

#define PB push_back

#define FOR(prom,a,b) for( ll prom = (a); prom < (ll)(b); ++prom )
#define F(a) FOR(i,0,a)
#define FF(a) FOR(j,0,a)

#define EPS (1e-10)
#define INF ((1<<30)-1)

#define EQ(a,b) (fabs(a-b)/fabs(a+b) < EPS)
struct Edge;
typedef list<Edge>::iterator iter;

struct Edge{
	int next_vertex;
	iter reverse_edge;
	Edge(int next_vertex):next_vertex(next_vertex){}
};


const int max_vertices=52;
int num_vertiecs;
list<Edge> adj[max_vertices];

vector<int> path;

void find_path(int v){
	while(adj[v].size()>0){
		int vn=adj[v].front().next_vertex;
		adj[vn].erase(adj[v].front().reverse_edge);
		adj[v].pop_front();
		find_path(vn);
	}
	path.push_back(v);
}

void add_edge(int a, int b){
	adj[a].push_front(Edge(b));
	iter ita=adj[a].begin();
	adj[b].push_front(Edge(a));
	iter itb=adj[b].begin();
	ita->reverse_edge =itb;
	itb->reverse_edge=ita;
}

string arr[55];
int main ()
{
	ios::sync_with_stdio(false);
	int N;
	while(cin>>N){
		F(55)
			arr[i]="";
		F(N){
			cin>>arr[i];
		}
		F(N){
			for(int j=i+1;j<N;j++){
				for(int k=0;k<arr[j].length();k++){
					if(arr[i].find(arr[j][k])!=string::npos){
						add_edge(i, j);
					}
				}
			}	
		}
		bool OK=false;
		F(N){
			path.clear();
			find_path(i);
			if(path.size()>=N){
				OK=true;
				break;
			}
		}
		cout<<(OK?"YES":"NO")<<endl;
	}

	return 0;
}