#include <iostream>
#include <vector>

using namespace std;

int maxLength = 0;

vector<vector<int>> adj;
vector<int> depth;

void dfs(int currNode)
{
    for(int newNode : adj[currNode]){
        if(depth[newNode] != -1){
            maxLength = max(maxLength, depth[currNode] - depth[newNode] + 1);
        }
        else{
            depth[newNode] = depth[currNode] + 1;
            dfs(newNode);
        }
    }
}

int main()
{
    int N, M;
    cin >> N >> M;

    adj.resize(N+1);
    depth.assign(N+1, -1);

    int a, b;
    for(int i = 0; i < M; ++i){
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    depth[1] = 0;
    dfs(1);
    cout << maxLength;
    return 0;
}