20pts求救！

#include<bits/stdc++.h>
using namespace std;
struct node
{
    vector<int> in;
    vector<int> out;
};
node tree[100005];
int maxx=0;
int l=1;
void dfs(int num)
{
	l++;
    if(tree[num].out.size()==0)
    {
        if(l>=maxx) maxx=l;
        l=1;
        return;
    }
    for(int i=1;i<=(tree[num].out).size();i++)
    {
        dfs(tree[num].out[i]);
    }
    return;
}
int main()
{
    int n;
    cin>>n;
    for(int i=1;i<=n-1;i++)
    {
        int a1,a2;
        cin>>a1>>a2;
        (tree[a1].out).push_back(a2);
        (tree[a2].in).push_back(a1);
    }
    dfs(1);
    cout<<maxx<<endl;
    return 0;
}