int x[1d5],y[1d5],z[1d5];
graph g;
deque<int> q;
{
	ll@n;
	rd((x--,y--)(n-1));
	g.setEdge(n,n-1,x,y);
	z[0..n-1]=-1;
	rep(i,n){
		if(i==0||g.es[i]==1){
			q.push_back(i);
			z[i]=0;
		}
	}
	while(!q.empty()){
		int i=q.front();
		q.pop_front();
		rep[g.edge[i]](j,g.es[i]){
			if(z[j]<0){
				q.push_back(j);
				z[j]=z[i]+1;
			}
		}
	}
	wtLn(z(n));
}