#include<iostream>
using namespace std;
int main()
{
int n,max=0;
cin>>n;
int l[n+2],r[n+2],f[n+2],s[n+2];
s[1]=1;
for(int i=1;i<=n;i++)
{
cin>>l[i]>>r[i];
if(l[i]!=0||r[i]!=0)
{
f[l[i]]=i;
f[r[i]]=i;
s[l[i]]=s[i]+1;
s[r[i]]=s[i]+1;
}
else
{
if(s[i]>=max)
{
max=s[i];
}
}
}
cout<<max;
return 0;
}
谢大佬