神奇RE爆0

#include<bits/stdc++.h>
#define pass 0
using namespace std;
int maxn,maxd;
int n,u,v;
vector<int> tre[114514];

int dfs(int child,int father,int childdis) {
    maxn<childdis?maxn=childdis,maxd=child:maxn=maxn;
    //cout<<child<<" "<<father<<" "<<childdis<<endl;
    for(int i:tre[child]) {
        if (i==father) continue;
        dfs(i,child,childdis+1);
    }
}

int main()
{
    cin>>n;
    for(int i=1;i<=n-1;i++) {
        cin>>u>>v;
        tre[u].push_back(v);
        tre[v].push_back(u);
    }
    dfs(1,-1,0);
    maxn=0;
    dfs(maxd,-1,0);
    cout<<maxn;
}