#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