TUMSO-17: Network

#include <bits/stdc++.h>

using namespace std;
const int N = 1e5;
vector <int> g[N + 10];
bool vs[N + 10];
int ans;

int dfs(int u, int p){
    vs[u] = true;
    vector <int> nxt;
    for(auto v: g[u]){
        if(v != p) nxt.push_back(dfs(v, u));
    }
    sort(nxt.begin(), nxt.end(), greater <int> ());
    int mx = 0, sz = nxt.size();
    for(int i=0;i<sz;i++)
        mx = max(mx, nxt[i] + i + 1);
    return mx;
}

int main(){

    int n, st;
    scanf("%d %d", &n, &st);

    for(int i=1;i<=n-1;i++){
        int u, v;
        scanf("%d %d", &u, &v);
        g[u].push_back(v);
        g[v].push_back(u);
    }

    cout << dfs(st, -1);

    return 0;
}