sicily 1021. Couples

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

int couple_relation[200005];

int main() {
    int t1, t2, n,i;
    while (scanf("%d", &n) && n!=0) {
        stack<int> s;
        for (i=0; i<n; i++) {
            cin>>t1>>t2;
            couple_relation[t1] = t2;
            couple_relation[t2] = t1;
        }
        for (i=1; i<=2*n; i++) {
            if (s.empty()) {
                s.push(i);
            }else if(couple_relation[i] == s.top())
                s.pop();
            else
                s.push(i);
        }
        if (s.empty())
            cout << "Yes" << endl;
        else
            cout << "No" << endl;
    }
    return 0;
}