#pragma region Macros
#include <bits/stdc++.h>
using namespace std;
template <class T> inline bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> inline bool chmin(T &a, T b) {
    if(a > b) {
        a = b;
        return 1;
    }
    return 0;
}
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args> void debugg(const T &x, const Args &...args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif

struct Setup {
    Setup() {
        cin.tie(0);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
    }
} __Setup;

using ll = long long;
#define OVERLOAD3(_1, _2, _3, name, ...) name
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define REP1(i, n) for(int i = 0; i < int(n); i++)
#define REP2(i, a, b) for(int i = (a); i < int(b); i++)
#define REP(...) OVERLOAD3(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define UNIQUE(v) sort(ALL(v)), (v).erase(unique(ALL(v)), (v).end())
#define SZ(v) ((int)(v).size())
const int INF = 1 << 30;
const ll LLINF = 1LL << 60;
constexpr int MOD = 1000000007;
constexpr int MOD2 = 998244353;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};

void Case(int i) { cout << "Case #" << i << ": "; }
int popcount(int x) { return __builtin_popcount(x); }
ll popcount(ll x) { return __builtin_popcountll(x); }
#pragma endregion Macros

using P = pair<int, int>;

int main() {
    int N, M;
    cin >> N >> M;
    if(M == 0) {
        cout << 5 << endl;
        return 0;
    }
    vector<vector<int>> G(N);
    set<P> se;
    REP(i, M) {
        int u, v;
        cin >> u >> v;
        u--, v--;
        G[u].push_back(v);
        G[v].push_back(u);
        se.emplace(u, v);
    }
    // REP(i, N) sort(RALL(G[i]));

    auto get_E = [&](int a, int b) -> P {
        if(a > b) swap(a, b);
        return P(a, b);
    };
    
    vector<bool> seen(N, false);
    REP(i, N) {
        if(SZ(G[i]) == 0) continue;
        if(seen[i]) continue;
        vector<pair<int, int>> rec;
        vector<P> kouho;
        auto dfs = [&](auto self, int u, int p) -> void {
            debug(i, p, u);
            seen[u] = true;
            for(int v : G[u]) {
                if(v == p) continue;
                if(!se.count(get_E(u, v))) continue;
                kouho.emplace_back(get_E(u, v));
                if(seen[v]) {
                    if(SZ(kouho) >= 3) {
                        for(auto e : kouho) {
                            debug(e);
                            se.erase(e);
                        }
                    }
                    kouho.clear();
                } else {
                    self(self, v, u);
                }
                if(SZ(kouho)) kouho.pop_back();
            }
        };
        dfs(dfs, i, -1);
    }
    if(se.empty()) cout << 4 << endl;
    else cout << 5 << endl;
}