#include <fstream>
#include <queue>
#include <cstring>
#include <vector>
using namespace std;
ifstream cin("darb.in");
ofstream cout("darb.out");
int n;
vector<int> v[100001];

queue<int> q;
int use[100001];
int last;
void bfs(int pos)
{
    q.push(pos);
    memset(use,-1,sizeof(use));
    use[pos]=0;

    while(q.size()>0)
    {
        for(int i=0;i<v[q.front()].size();i++)
        {
            if(use[v[q.front()][i]]==-1)
            {
                q.push(v[q.front()][i]);
                use[v[q.front()][i]]=use[q.front()]+1;
            }
        }
        last=q.back();
        q.pop();
    }
}
int main()
{
    int x,y;
    while(cin>>x>>y)
    {
        v[x].push_back(y);
        v[y].push_back(x);
    }
    bfs(1);
    bfs(last);
    cout<<use[last]+1;
    return 0;
}