#include<bits/stdc++.h>
using namespace std;
int n,max_deep=1;
int deep[100005];
int main(){
    cin>>n;
    deep[1]=1;
    for(int i=1;i<=n;i++)
    {
        int a,b;
        cin>>a>>b;
        if(a!=0)deep[a]=deep[i]+1;
        if(b!=0)deep[b]=deep[i]+1;
        max_deep=max(max_deep,max(deep[a],deep[b]));
    }
    cout<<max_deep<<endl;
    return 0;
}

WA 第二个点：

Wrong Answer.wrong answer On line 1 column 1, read 8, expected 4.