// Problem: AD - W7P1: F*** 3-Colorable Graphs
// Contest: Virtual Judge - 602 - Season 2023 - HW Series 1
// URL: https://vjudge.net/contest/570461#problem/AD
// Memory Limit: 253 MB
// Time Limit: 1000 ms
// 
// Powered by CP Editor (https://cpeditor.org)


#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <immintrin.h>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <variant>
using namespace std;

//numbers
using ll=long long;
#define int ll
using ld=long double;
//pairs
#define P pair
#define pi P<int,int>
#define ff first
#define ss second
#define mp make_pair
//std data structure
#define all(x) begin(x), end(x)
#define sz(x) (int) (x).size()
//vectors
#define V vector
#define vi V<int>
#define v2i V<vi>
#define v3i V<v2i>
#define vpi V<pi>
#define vsi V<si>
#define pb push_back
//sets
#define S set
#define MS multiset
#define US unordered_set
#define si S<int>
#define msi MS<int>
#define usi US<int>
#define ins insert
#define era erase
//maps
#define M map
#define UM unordered_map
#define mii M<int,int>
#define mivi UM<int,vi>
#define misi UM<int,si>
#define umii UM<int,int>
#define umivi UM<int,vi>
#define umisi UM<int,si>
//queues
#define Q queue
#define PQ priority_queue
#define qi Q<int>
#define qpi Q<pi>
#define pqi PQ<int>
#define rpqi PQ<int,vi,greater<int> >
#define pqpi PQ<pi>
#define rpqpi PQ<pi,vpi,greater<pi> >
//constants
const int MOD=998244353;
const int INF=922337203685477580;
//nt functions
int binpow(int a, int b, int m=MOD) {
    a%=m; int res=1;
    while (b>0) {
        if (b&1) res=res*a%m;
        a=a*a%m;
        b>>=1;
    }
    return res;
}
int gcd (int a, int b) {
    return b?gcd (b,a%b):a;
}
int lcm (int a, int b) {
    return a/gcd(a,b)*b;
}
int inv(int i, int m=MOD) {
	return binpow(i, m-2, m);
}
//new header wip

int n,m;
vi deg;
v2i adj;
vi g1;
V<bool> vis;

void dfs0(int p, int g) {
	if (vis[p]) return;
	vis[p]=1;
	if (g) g1.pb(p);
	for (auto i:adj[p]) {
		dfs0(i,(g+1)%2);
	}
}

signed main() {
	ios::sync_with_stdio(false); cin.tie(nullptr);
	cin>>n>>m; n*=2; adj=v2i(n); deg=vi(n,0);
	while (m--) {
		int u,v; cin>>u>>v; u--; v--;
		deg[u]++; deg[v]++;
		adj[u].pb(v); adj[v].pb(u);
	}
	
	for (auto i:deg) {
		if (i>=3) {
			cout<<2; return 0;
		}
	}
	
	if (n>6) {
		assert(false);
	}
	
	for (int i=0; i<n; i++) {
		sort(all(adj[i]));
	}
	
//each node connected to at most 2 vertices
	//create groups
	vis=V<bool>(n,0);	
	dfs0(0,0);
	
	for (auto i:g1) {
		for (auto j:g1) {
			if (i==j) continue;
			if (min(sz(adj[i]),sz(adj[j]))<2) continue;
			if (adj[i][0]==adj[j][0] && adj[i][1]==adj[j][1]) {
				cout<<2; return 0;
			}
		}
	}
	cout<<3;
	return 0;
}