记录编号	594848	评测结果	AAAAAAAAAA
题目名称	消防演练	最终得分	100
用户昵称	┭┮﹏┭┮	是否通过	通过
代码语言	C++	运行时间	0.522 s
提交时间	2024-10-05 20:08:38	内存使用	11.92 MiB

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define fi first
#define in inline
#define se second
#define mp make_pair
#define pb push_back
const int N = 2e5+10;

ll read(){
	ll x = 0,f = 1;char c = getchar();
	for(;c < '0' || c > '9';c = getchar())if(c == '-')f = -1;
	for(;c >= '0' && c <= '9';c = getchar())x = (x<<1) + (x<<3) + c-'0';
	return x * f;
}


int n;
vector<int>e[N];


int f[N],g[N],ans;
void dfs(int x,int fa){
	for(int y : e[x]){
		if(y == fa)continue;
		dfs(y,x);
		f[x] = max(f[x],f[y] + (int)e[x].size() - 2);
	}
	f[x] = max(f[x],(int)e[x].size() - 1);
	ans = max(ans,f[x]);
}
void dfs2(int x,int fa){
	for(int y : e[x]){
		if(y == fa)continue;
		dfs2(y,x);
		ans = max(ans,g[x] + f[y] + (int)e[x].size() - 2);
		g[x] = max(g[x],f[y]);
	}
}


int main(){
	freopen("drill.in","r",stdin);
	freopen("drill.out","w",stdout);
	n = read();
	for(int i = 1;i < n;i++){
		int x = read(),y = read();
		e[x].pb(y),e[y].pb(x);
	}
	if(n == 2)return printf("0\n"),0;
	dfs(1,0);
//	for(int i = 1;i <= n;i++)printf("%d ",f[i]);
//	printf("\n");
//	printf("%d\n",ans);
	dfs2(1,0);
	printf("%d\n",ans);

	return 0;

}