1 #include <stdio.h>
 2 #include <algorithm>
 3 #include <string.h>
 4 #include <iostream>
 5 #include <vector>
 6 #include <map>
 7 #include <queue>
 8 #include <set>
 9 #include <vector>
10 #include <string>
11 #include <sstream>
12 using namespace std;
13 
14 int father[100005];
15 int a[100005];
16 int MAXH, MINH;
17 
18 int findroot(int p)
19 {
20     int r, x, j;
21     r=p;
22     while(r!=father[r])
23     r=father[r];
24     x=p;
25     while(x!=r)
26     {
27         j=father[x];
28         father[x]=r;
29         x=j;
30     }
31     return r;
32 }
33 
34 main()
35 {
36     int x, y, i, j, k, num, flag=1;
37     for(i=1;i<=100005;i++) father[i]=i;
38     num=0;
39     set<int>se;
40     while(scanf("%d %d",&x,&y)==2&&x!=-1)
41     {
42         if(x==0&&y==0)
43         {
44             if(!flag)
45             {
46                 printf("No\n");
47                 for(i=1;i<=100005;i++) father[i]=i;
48                 se.clear();
49                 flag=1;continue;
50             }
51             set<int>::iterator it;
52             for(it=se.begin();it!=se.end();it++)
53             if((*it)==findroot(*it))
54             num++;
55             se.clear();
56             if(num>1) {
57                 printf("No\n");
58             }
59             else printf("Yes\n");
60             num=0;
61             for(i=1;i<=100005;i++) father[i]=i;
62             continue;
63         }
64         int fx=findroot(x);
65         int fy=findroot(y);
66         se.insert(x);
67         se.insert(y);
68         if(fx!=fy)
69         {
70             if(fx>fy) swap(fx,fy);
71             father[fy]=fx;
72         }
73         else flag=0;
74     }       
75 }