diametro.cpp

#include <cstdio>
#include <vector>

constexpr int maxn = 2e5+10;

std::vector<int> g[maxn];

int ans;

int max(int a, int b) { return a > b ? a : b; }

int dfs(int u, int p) {
	int ff = 0, ss = 0;
	for(int v : g[u]) if(v != p) {
		int val = dfs(v, u);
		if(val > ff) ss = ff, ff = val;
		else if(val > ss) ss = val;
	}
	ans = max(ans, ff + ss);
	return ff+1;
}

int main() {
	int n; scanf("%d", &n);
	for(int i = 1, a, b; i < n; i++)
		scanf("%d %d", &a, &b), g[a].push_back(b), g[b].push_back(a);
	dfs(1, 0);
	printf("%d\n", ans);
}