#include <bits/stdc++.h>
using namespace std;
vector<vector<int> > g;
vector<int> d;
int op = 0;

void dfs(int v){
    for (int x : g[v]){
        if (d[x] < 0){
            d[x] = d[v] + 1;
            dfs(x);
        }
        else if (d[x] != d[v] - 1){
            op = max(op, d[v] - d[x] + 1);
        }
    }
}

int main()
{
    int n, m;
    cin >> n >> m;
    g.resize(n+1);
    d.assign(n+1, -1);
    while (m--){
        int a, b;
        cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    d[1] = 0;
    dfs(1);
    cout << op;
}