#include<iostream>
#include<string>
#include<set>
#include<cstdio> 
using namespace std;
int main()
{
    set<string>shu,ying;
    string a1,a2;
    int i,n;
    set<string>::iterator k;
    while(scanf("%d",&n),n)
    {
        shu.clear();
        ying.clear();
        for(i=1;i<=n;i++)
        {
            cin>>a1>>a2;
            ying.insert(a1);
            shu.insert(a2);
        }
        for(k=shu.begin();k!=shu.end();k++)
        {
            if(ying.count(*k))
                ying.erase(*k);
        }
        if(ying.size()==1)
            printf("Yes\n");
        else
        printf("No\n");
    }
    return 0;
}