1131 - Tree Diameter

using namespace std;
using ll = long long;
using ii = pair<int, int>;
using vi = vector<int>;
int const NMAX = 2e5 + 11;
int n;
vi g[NMAX];
ii dfs(int u, int p, int d)
{
    ii ans = {d, u};
    for (auto v : g[u])
    {
        if (v == p)
            continue;
        ans = max(ans, dfs(v, u, d + 1));
    }
    return ans;
}
int main(void)
{
    cin >> n;
    for (int i = 0; i < n - 1; ++i)
    {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
        g[v].push_back(u);
    }
    auto [d1, u] = dfs(1, 0, 0);
    auto [d2, v] = dfs(u, 0, 0);
    cout << d2 << endl;
    return 0;
}