#include<bits/stdc++.h>
#define rt register int
using namespace std;int ans,x,y,num,f[100010];
int main()
{
	while(x!=-1&&y!=-1)
	{
	    scanf("%d%d",&x,&y);if(x==-1&&y==-1)return 0;
		while(x&&y){f[x]=f[y]=1;scanf("%d%d",&x,&y);++num;}
		for(rt i=1;i<=100010;++i) if(f[i]) ++ans;
		if(ans-1==num) printf("1\n");
		else printf("0\n");
		memset(f,0,sizeof(f));ans=num=0;
	}return 0;
}
/*
6 8  5 3  5 2  6 4
5 6  0 0
8 1  7 3  6 2  8 9  7 5
7 4  7 8  7 6  0 0
3 8  6 8  6 4
5 3  5 6  5 2  0 0
-1 -1
*/