#include <iostream>
#include <cmath>
using namespace std;

int n, m, L[1001], ln = 2;
bool a[1001][1001];

void bejar(int k) {
    for(int i = 1; i <= n; i++) {
        if(a[k][i]) {
            if(L[i] == -1) {
                L[i] = L[k]+1;
                bejar(i);
            } else if(abs(L[i] - L[k])+1 > ln)
                ln = abs(L[i] - L[k])+1;
        }
    }
}

int main()
{
    cin >> n >> m;
    for(int i = 0; i < m; i++) {
        int x, y;
        cin >> x >> y;
        a[x][y] = true; a[y][x] = true;
    }

    for(int i = 1; i <= n; i++) L[i] = -1;
    L[1] = 0;
    bejar(1);
    cout << ln;

    return 0;
}