#include <iostream>
#define ll long long
#include <vector>
#include <deque>

using namespace std;

ll n,m,i,j,a,b,maxi=0;

struct element
{
    bool seen=false;
    vector <ll> sz;
};

vector <element> x;

deque <ll> v;

void DFS (ll curr)
{
    x[curr].seen=true;
    for (auto &e:x[curr].sz)
    {
        if (!x[e].seen)
        {
            v.push_front(e);
            DFS(e);
        }
        else
        {
            ll db=0;
            while(!v.empty()&&v[0]!=e)
            {
                db++;
                v.pop_front();
            }
            //if (!v.empty()) v.pop_front();
            if (db+1>maxi) maxi=db+1;
            if (x[curr].sz.size()>2) v.push_front(curr);
        }
    }
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);

    cin>>n>>m;
    x.resize(n+1);
    for (i=1;i<=m;++i)
    {
        cin>>a>>b;
        x[a].sz.push_back(b);
        x[b].sz.push_back(a);
    }

    v.push_back(1);
    DFS(1);
    cout<<maxi;

    return 0;
}