// kaktuszgraf.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <vector>
#include <deque>
#include <cmath>

using namespace std;

struct adat
{
    int lat,tav;
    vector<int>sz;
};

int n, a, b, i, maxi,bejart[1001][1001],m;
vector<adat>x;
void melysegi(int csp)
{
    x[csp].lat = 1;
    for (auto& e : x[csp].sz)
    {
        if (!x[e].lat)
        {
            bejart[csp][e] = bejart[e][csp] = 1;
            x[e].tav = x[csp].tav + 1;
            melysegi(e);
        }
        else
        {
            if (!bejart[csp][e])
            {
                if (maxi < abs(x[csp].tav - x[e].tav) + 1)
                    maxi = abs(x[csp].tav - x[e].tav) + 1;
            }
            else bejart[csp][e] = bejart[e][csp] = 1;
        }
    }
}

int main()
{
    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);
    }
    melysegi(1);
    cout << maxi;

    return 0;
}
/*
13 15
1 3
1 4
2 3
3 5
4 5
4 12
12 13
13 4
5 7
7 6
7 11
6 8
11 10
10 9
8 9

*/
// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

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//   2. Use the Team Explorer window to connect to source control
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//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file