#include<stdio.h>
#include<math.h>
#include<string.h>
#include<stdlib.h>
#include <ctype.h>
struct  node{
  int lc,rc;
   }btnode[1000000];
int deep=0;
int ans=1;
void dfs(struct node t)
{
	deep++;
	if(t.lc==0&&t.rc==0) 
	{
		if(deep>ans) ans=deep;
		deep--;
		return ;
	}
	dfs(btnode[t.lc]);
	dfs(btnode[t.rc]);
}
int main()
{
	int i,n;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	{
		scanf("%d%d",&btnode[i].lc,&btnode[i].rc);
	}
	dfs(btnode[1]);
	printf("%d",ans);
	return 0;
}

不知哪里有问题只能过2个测试点...