#pragma once
#pragma execution_character_set("utf-8")
// 本文件为utf-8 编码格式#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
#define N 100005
int dp[N][2];
struct Edge{int to;int next;
};
Edge gEdges[2*N];
int gHead[N];
bool gVisited[N];
int gEdgeIndex;
void InsertEdge(int u, int v){int e = gEdgeIndex++;gEdges[e].to = v;gEdges[e].next = gHead[u];gHead[u] = e;e = gEdgeIndex++;gEdges[e].to = u;gEdges[e].next = gHead[v];gHead[v] = e;
}pair<int, int> dfs(int root){if (dp[root][0] != -1 && dp[root][1] != -1){return pair<int, int>(dp[root][0], dp[root][1]);}gVisited[root] = true;int e = gHead[root];int max1 = 0, max2 = 0, max = 0, child_num = 0;for (; e != -1; e = gEdges[e].next){int v = gEdges[e].to;if (!gVisited[v]){pair<int, int> result = dfs(v);max = max > result.first ? max : result.first;if (max1 >= result.second){max2 = max2 > result.second ? max2 : result.second;}else{//求一组数中的第一大和第二大的数！！！ 注意次序/*//这样做，在处理第一个result的时候， max1和max2赋值为同一个...errormax1 = result.second;max2 = max1;//这样做，考虑到第一个值的处理，但是 对max1和max2的更新次序错了。 仔细考虑...max1 = result.second;if(max1 != 0)max2 = max1;*/if (max1 != 0)max2 = max1;max1 = result.second;}child_num++;}}if (child_num == 0)dp[root][0] = dp[root][1] = 0;else if (child_num == 1){dp[root][0] = max;dp[root][1] = 1 + max1;}else{dp[root][1] = 1 + max1;dp[root][0] = max > (2 + max1 + max2) ? max : (2 + max1 + max2);      }return pair<int, int>(dp[root][0], dp[root][1]);
}void Init(){memset(gVisited, false, sizeof(gVisited));memset(gHead, -1, sizeof(gHead));gEdgeIndex = 0;memset(gEdges, -1, sizeof(gEdges));memset(dp, -1, sizeof(dp));
}
int main(){int n, u, v;scanf("%d", &n);Init();for (int i = 1; i < n; i++){scanf("%d %d", &u, &v);InsertEdge(u, v);}pair<int, int> result = dfs(1);printf("%d\n", result.first>result.second ? result.first : result.second);return 0;
}