// . . . Bismillahir Rahmanir Rahim . . .

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#ifndef ONLINE_JUDGE
#define dbg_out cout
#define debug(...) dbg_out << "DBG )> "; __f(#__VA_ARGS__, __VA_ARGS__);
template<typename T1, typename T2> ostream& operator<<(ostream& out, pair<T1, T2> pr) { out << "{ " << pr.first << ", " << pr.second << " }"; return out; }
template<typename T1> ostream& operator<<(ostream& out, vector<T1> vec) { out << "{ "; for (auto &x: vec) out << x << ", "; out << "}"; return out; }
template<typename T1, size_t size> ostream& operator<<(ostream& out, array<T1, size> arr) { out << "{ "; for (auto &x: arr) out << x << ", "; out << "}"; return out; }
template<typename T1, typename T2> ostream& operator<<(ostream& out, map<T1, T2> mp) { out << "{ ";for (auto &x: mp) out << x.first << ": " << x.second <<  ", "; out << "}"; return out; }
template <typename Arg1> void __f(const char* name, Arg1&& arg1) { while (isspace(name[0])) name++; (isalpha(name[0]) || name[0] == '_') ? dbg_out << name << ": " << arg1 << "\n" : dbg_out << arg1 << "\n"; dbg_out.flush();}
template <typename Arg1, typename... Args> void __f (const char* names, Arg1&& arg1, Args&&... args) { const char *comma = strchr(names + 1, ','); while (isspace(names[0])) names++; (isalpha(names[0]) || names[0] == '_') ? dbg_out.write(names, comma - names) << ": " << arg1 << " | " : dbg_out << arg1 << " | "; __f(comma + 1, args...);}
#else
#define debug(...)
#endif

ll gcd(ll a, ll b){ while (b){ a %= b; swap(a, b);} return a;}
ll lcm(ll a, ll b){ return (a/gcd(a, b)*b);}
ll ncr(ll a, ll b){ ll x = max(a-b, b), ans=1; for(ll K=a, L=1; K>=x+1; K--, L++){ ans = ans * K; ans /= L;} return ans;}
ll bigmod(ll a,ll b,ll mod){ if(b==0){ return 1;} ll tm=bigmod(a,b/2,mod); tm=(tm*tm)%mod; if(b%2==1) tm=(tm*a)%mod; return tm;}
ll egcd(ll a,ll b,ll &x,ll &y){ if(a==0){ x=0; y=1; return b;} ll x1,y1; ll d=egcd(b%a,a,x1,y1); x=y1-(b/a)*x1; y=x1; return d;}
ll modpow(ll a,ll p,ll mod) {ll ans=1;while(p){if(p%2)ans=(ans*a)%mod;a=(a*a)%mod;p/=2;} return ans;}
ll inverse_mod(ll n,ll mod) {return modpow(n,mod-2,mod);}


const int N = 1e4;
vector<int> ara[2*N+5];
bool dp[2*N+5][4];

bool calc(int at, int p, int x, int h)
{
	if(dp[at][h]) return 0;
	
	dp[at][h] = 1;
	if(h == 3){
		//cout << at << ' ' << h << "\n";
		for(int v : ara[at]){
			if(x == v) return true;
		}
		
		return false;
	}
	
	//cout << at << ' ' << h << "\n";
	//cout << at << ' ' << h << "\n";
	
	bool ok = 0;
	for(auto v : ara[at]){
		if(v != p){
			ok |= calc(v, at, x, h+1);
			if(ok) return ok;
		}
	}
	
	return 0;
}

int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	memset(dp, 0, sizeof dp);
	
	int n, m; cin >> n >> m;
	
	for(int K = 0; K < m; K++){
		int a, b; cin >> a >> b;
		
		ara[a].push_back(b);
		ara[b].push_back(a);
	}
	
	bool ok = 0;
	
	for(int K = 1; K <= n; K++){
		ok |= calc(K, K, K, 0);
		if(ok) break;
	}
	
	if(ok) cout << 2 << "\n";
	else cout << 3 << "\n";
	
	return 0;
}