TUMSO17: Network

#include <bits/stdc++.h>
using namespace std;

const int N = 1e5 + 5;

vector<int> adj[N];
int dp[N];

void DFS(int u, int p){
    int mx = 0;
    vector<int> tme;
    for(int v : adj[u]){
        if(v == p){
            continue;
        }
        DFS(v, u);
        tme.push_back(dp[v]);
    }
    sort(tme.begin(), tme.end(), greater<int>());
    for(int i = 0; i < tme.size(); ++i){
        mx = max(mx, tme[i] + i + 1);
    }
    dp[u] = mx;
}

int main(){

    int nVertex, rt;
    scanf("%d%d", &nVertex, &rt);
    for(int i = 1; i < nVertex; ++i){
        int u, v;
        scanf("%d%d", &u, &v);
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    DFS(rt, 0);
    cout << dp[rt];

    return 0;
}