http://lerna.pro/contests/337/4

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
using namespace std;
vector<vector <int>> way;
vector<bool> used;
vector<int> ans;
int cur_mx;
int dfs(int pos)
{
	for (int i = 0; i < way[pos].size(); i++)
		if (used[way[pos][i]])
		{
			used[way[pos][i]] = false;
			ans[way[pos][i]] = ans[pos] + 1;
			dfs(way[pos][i]);
		}
	if (ans[pos] > cur_mx)
		cur_mx = ans[pos];
	return cur_mx;
}

int main()
{
	int n;
	scanf("%d", &n);
	way.resize(n + 1);
	for (int i = 0; i < n - 1; i++)
	{
		int a, b;
		scanf("%d %d", &a, &b);
		way[a].push_back(b);
		way[b].push_back(a);
	}
	int mx = 0;
	for (int i = 1; i <= n; i++)
	{
		cur_mx = 0;
		ans.resize(n + 1, 1);
		used.resize(n + 1, true);
		int t = dfs(i);

		if (mx < t)
			mx = t;
	}

	printf("%d", mx);
	return 0;
}