#include <iostream>
#include <string>
using namespace std;

int main()
{
    int pairs = 0;
    int l = 0;
    int only1pair=0;
    string answer="";

    while(cin>>l)
    {
        string *input=new string[l];
        for(int i =0;i<l;i++)
        {

            cin>>input[i];

        }
        for(int i=0;i<l;i++)
        {
            for(int j=0;j<l;j++)
            {
                if (pairs<3)
                {
                    if (input[i][0] == input[j][0]||input[i][1] == input[j][1])
                    {
                        pairs++;

                    }
                }
                else
                {
                    break;
                }
            }
            pairs--;
            //counted all pairs for input[i]
            if (pairs == 1)
            {
                only1pair++;
            }
            else if (pairs==0)
            {
                answer = "NO";

                break;

            }

            pairs = 0;
        }
        if (only1pair > 2||answer!="")
        {
            answer = "NO";
        }
        else
        {
            answer = "YES";
        };

        cout<<answer<<endl;
        answer = "";
        only1pair = 0;
    };

    return 0;
}