#include <iostream>

 #include <stack>

 using namespace std;

 int main() {

     int num;

     while (cin >> num && num) {

         int *store = new int[num*+];

         for (int i = ; i <= num; i++) {

             int a, b;

             cin >> a >> b;

             store[a] = store[b] = i;

         }

         stack<int> st;

         for (int i = ; i <= num*; i++) {

             if (!st.empty() && st.top() == store[i]) {

                 st.pop();

             }

             else {

                 st.push(store[i]);

             }

         }

         st.empty() ? cout << "Yes\n" : cout << "No\n";

     }

     return ;

 }