#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <set>
#include <algorithm>
#include <limits.h>
#include <string.h>
#include <sstream>

int main(int argc, char* argv[])
{
	std::ios_base::sync_with_stdio(false);

	int n;
	while ((std::cin >> n).eof() == false)
	{
		std::vector<std::pair<std::string, std::string> > edges;
		std::vector<std::string> points;

		std::string card;
		std::map<std::string, int> pointNum;
		for (int i = 0; i < n; ++i)
		{
			std::cin >> card;

			pointNum.insert({card,i});
			
			for (int j = 0; j < points.size(); ++j)
			{
				if (points[j][0] == card[0] || points[j][1] == card[1])
				{
					edges.push_back({ card, points[j] });
					edges.push_back({ points[j], card });
				}
			}
			points.push_back(card);
		}

		/*for (auto &edge : edges)
		{
			std::cout << edge.first << " -> " << edge.second << std::endl;
		}*/

		std::map<std::string, std::vector<std::string> > graph;

		for (auto &edge : edges)
		{
			graph[edge.first].push_back(edge.second);
		}
		bool yes = false;
		for (auto a : graph)
		{
			bool visitedPoints[52];
			int counters[52];
			int depth = 0;
			std::string curPoint[53];
			curPoint[0] = a.first;
			memset(visitedPoints,false,sizeof(bool)*52);
			memset(counters, 0, sizeof(int)*52);
			while (depth >= 0)
			{
				auto vektor = graph[curPoint[depth]];
				int vis = pointNum[vektor[counters[depth]]];
				if (!visitedPoints[vis])
				{
					visitedPoints[vis] = true;
					std::string temp = vektor[counters[depth]];
					counters[depth]++;
					depth++;
					if (depth == n)
					{
						yes = true;
						break;
					}
					curPoint[depth] = temp;
				}
				else
				{
					counters[depth]++;
				}
				while (depth > -1 && counters[depth] == graph[curPoint[depth]].size())
				{
					visitedPoints[pointNum[curPoint[depth]]] = false;
					counters[depth] = 0;
					depth--;
				}
			}
			if (yes)
				break;
		}
		if (yes)
		{
			std::cout << "YES" << std::endl;
		}
		else
		{
			std::cout << "NO" << std::endl;
		}
	}

	return 0;
}