/*
 
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 _/    _/     _/      _/     _/    _/        _/       _/    _/     _/      _/            
  _/  _/      _/      _/      _/  _/         _/      _/      _/    _/_/  _/_/         
   _/_/       _/_/_/_/_/        _/           _/      _/      _/    _/  _/  _/          
  _/  _/      _/      _/        _/           _/      _/      _/    _/      _/          
 _/    _/     _/      _/        _/           _/       _/    _/     _/      _/          
_/      _/    _/      _/        _/           _/         _/_/       _/      _/       
 
*/
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
using i64 = long long;
#define rep(i,a,n) for(int i=a;i<n;i++)
#define per(i,a,n) for(int i=n-1;i>=a;i--)
#define fastio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define multi int _;cin>>_;while(_--)
#define debug(x) cerr << #x << " = " << (x) << endl;
#define int long long
#define pb push_back
#define eb emplace_back
ll gcd(ll a,ll b){ return b?gcd(b,a%b):a;}
mt19937_64 mrand(chrono::steady_clock().now().time_since_epoch().count());
int rnd(int l,int r){ return mrand() % (r - l + 1) + l;}
void test() {cerr << "\n";}
template<typename T, typename... Args> 
void test(T x, Args... args) {cerr << x << " ";test(args...);}
const ll MOD = 998244353;
// const ll MOD = 1e9+7;
ll ksm(ll x,ll y){ll ans=1;x%=MOD;while(y){if(y&1)ans=ans*x%MOD;x=x*x%MOD,y/=2;}return ans;}

const int P1 = 972152273, base1 = 809;
const int P2 = 905563261, base2 = 919;
const ll N = 200005;
//head

struct DSU {
    std::vector<int> f, siz;
    DSU(int n) : f(n), siz(n, 1) { std::iota(f.begin(), f.end(), 0); }
    int leader(int x) {
        while (x != f[x]) x = f[x] = f[f[x]];
        return x;
    }
    bool same(int x, int y) { return leader(x) == leader(y); }
    bool merge(int x, int y) {
        x = leader(x);
        y = leader(y);
        if (x == y) return false;
        siz[x] += siz[y];
        f[y] = x;
        return true;
    }
    int size(int x) { return siz[leader(x)]; }
};

signed main()
{  
#ifdef localfreopen
    // freopen("1.in","r",stdin);
#endif
    fastio
    std::cout << std::fixed << std::setprecision(10);
    
    int n, m;
    std::cin >> n >> m;
    std::vector<std::vector<int>> adj(2 * n + 1);
    
    std::vector<std::pair<int, int>> edges;
    
    for (int i = 1; i <= m; i++) {
    	int u, v;
    	std::cin >> u >> v;
    	adj[u].push_back(v);
    	adj[v].push_back(u);
    }
    
    std::vector<int> from(2 * n + 1), vis(2 * n + 1);
    std::queue<int> q;
    q.push(1);
    vis[1] = 1;
    
    while (!q.empty()) {
    	int x = q.front();
    	q.pop();
    	for (auto y : adj[x]) {
    		if (vis[y] == 1) {
    			if (from[from[y]] == from[x]) {
	    			std::cout << 2 << "\n";
	    			return 0;
    			}	
    			continue;
    		}
    		from[y] = x;
    		vis[y] = 1;
    		q.push(y);
    	}
    }
    std::cout << 3 << "\n";
    
    
    return 0;
}