#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <ctime>
#include <assert.h>
#include <chrono>
#include <random>
#include <numeric>
#include <set>
#include <deque>
#include <stack>
#include <sstream>
#include <utility>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
#include <tuple>
#include <array>
#include <bitset>
using namespace std;
typedef long long int ll;
typedef unsigned long long ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

struct UnionFind{
    vector<int> par,num;
    vector<int> mx;
    UnionFind(int n):par(n),num(n,1),mx(n,0){
        iota(par.begin(),par.end(),0);  //include<numeric>
    }
    int find(int v){
        return (par[v]==v)?v:(par[v]=find(par[v]));
    }
    void unite(int u,int v){
        u=find(u),v=find(v);
        if(num[u]<num[v])swap(u,v);
        mx[u] = max(mx[u],mx[v])+1;
        if(u==v)return;
        num[u]+=num[v];
        par[v]=u;
    }
    bool same(int u,int v){
        return find(u) == find(v);
    }
    int size(int v){
        return num[find(v)];
    }
};


int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n,m; cin >> n >> m;
    vector<pair<int,int>> v(m);
    for(int i=0;i<m;i++){
        int a,b; cin >> a >> b;
        a--; b--;
        v[i] = {a,b};
    }
    UnionFind uf(n);
    for(int i=m-1;i>=0;i--){
        uf.unite(v[i].first, v[i].second);
    }
    cout << uf.mx[uf.find(0)] << endl;
}