#include<stdio.h>
#include<stdlib.h>
#include<iostream>
using namespace std; 
typedef struct BiTNode{
	int data;
	struct BiTNode *lchild,*rchild;
}BiTNode,*BiTree;
int creat(BiTree &T){
	int left,right;
	scanf("%d%d",&left,&right);
	if(left==0){
		T->lchild=NULL;
	}else{
		T->lchild=(BiTree)malloc(sizeof(BiTNode));
		T->lchild->data=left;
	}
	if(right==0){
		T->rchild=NULL;
	}else{
		T->rchild=(BiTree)malloc(sizeof(BiTNode));
		T->rchild->data=right;
	}
	if(T->lchild) creat(T->lchild);
	if(T->rchild) creat(T->rchild);
}
int depth(BiTree T){
	if(T==NULL) return 0;
	int ld=depth(T->lchild);
	int rd=depth(T->rchild);
	if(ld>rd) return ld+1;
	else return rd+1;
}
int main(){
	BiTree T;
	T=(BiTree)malloc(sizeof(BiTNode));
	T->data=1;
	int n;
	scanf("%d",&n);
	creat(T);
	printf("%d",depth(T));
}