#include<cstdio>
#define maxn 100000+100
using namespace std;
int f[maxn]={0};
int find(int x)
{
	if (f[x]!=x) {return f[x]=find(f[x]);}
		else return x;
}

int main()
{
	freopen("explosion.in","r",stdin);
	freopen("explosion.out","w",stdout);
	int u,v,ans=0;
	for (int i=0;i<=maxn;i++) f[i]=i;
	while(scanf("%d",&u)==1&&u!=-1)
	{
		scanf("%d",&v);
		if (find(u)!=find(v))
			f[f[u]]=f[v];
		else ans++;
	}
	printf("%d",ans);
	return 0;
}