sicily 1021. Couples

#include<iostream>
#include<stack>
#include<map>
#include<stdio.h>
using namespace std;
int main()
{
    int n, m1,m2,k;
    while(scanf("%d",&n)&&n)
    {
        map<int,int> m;
        stack<int> c;
        for(int i=0;i<n;i++)
        {
            scanf("%d%d",&m1,&m2);
            m[m1]=m2;
            m[m2]=m1;
        }
        for(k=1;k<=2*n;k++)
        {
            if(!c.empty()&&m[k]==c.top())
                c.pop();
            else    
                c.push(k);
        }
        if(c.empty())
            printf("Yes\n");
        else
            printf("No\n");
    }
    return 0;
}