#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, n) for (int i = a; i < (int)(n); i++)
using ll = long long;

int main()
{
    int n;
    cin >> n;
    vector<string> first(n), last(n);
    set<string> myojis;
    rep(i, 0, n)
    {
        cin >> first[i] >> last[i];
        myojis.insert(first[i]);
    }
    set<string> used;
    bool ok = true;
    rep(i, 0, n)
    {
        if (!myojis.count(first[i]))
        {
            continue;
        }
        else
        {
            if (used.count(last[i]))
            {
                ok = false;
                break;
            }
            used.insert(last[i]);
        }
    }
    cout << (ok ? "Yes\n" : "No\n");
}