求树的直径，两遍dfs即可

//蒟蒻的代码
#include<iostream>
#include <vector>

using namespace std;

const int N = 10000 + 10;

int n, c, d[N];
vector<int> e[N];//用vector存储树

void dfs(int u, int fa) {
  for (int v : e[u]) {
    if (v == fa)
      continue;
    d[v] = d[u] + 1;
    if (d[v] > d[c]) 
      c = v;
    dfs(v, u);
  }
}

int main() {
  scanf("%d", &n);
  //输入
  for (int i = 1; i < n; i++) {
    int x, y;
    cin >> x >> y;
    e[x].push_back(y);
    e[y].push_back(x);
  }
  //两遍dfs
  dfs(1, 0);
  d[c] = 0;
  dfs(c, 0);
  cout << d[c] << endl;
  return 0;
}