#include <iostream>
#include <vector>
#include <algorithm>
#include <set>

using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(n); i++)


int main(){
    int N,M; cin >> N >> M;
    int ans = 4;
    if(M == 0) ans += N % 2;
    else if(M == 1) ans = 5;
    else{
        set<pair<int,int>> uv;
        rep(i,M){
            int u,v; cin >> u >> v; u--; v--;
            uv.insert({ u,v });
        }
        while(uv.size()){
            set<int> u_v;
            for(auto [u,v] : uv){
                u_v.insert(u);
                u_v.insert(v);
            }
            vector<int> uvvec(u_v.begin(), u_v.end());
            rep(i,M-1) if(0 == uv.count({ uvvec[i],uvvec[i+1] })){ ans = 5; break; }
            if(0 == uv.count({ uvvec.front(), uvvec.back() })){ ans = 5; break; }
            rep(i,M-1) if((uvvec[i+1] - uvvec[i]) % 2 == 0){ ans = 5; break; }
            if((uvvec.front() + N - uvvec.back()) % 2 == 0){ ans = 5; break; }
            if(ans == 5) break;
            rep(i,M-1) uv.erase({ uvvec[i],uvvec[i+1] });
            uv.erase({ uvvec.front(), uvvec.back() });

            set<pair<int,int>> new_uv;
            for(auto [u,v] : uv){
                int nxu = upper_bound(uvvec.begin(), uvvec.end(), u) - uvvec.begin();
                int nxv = upper_bound(uvvec.begin(), uvvec.end(), v) - uvvec.begin();
                new_uv.insert({ nxu, nxv });
            }
            if(new_uv.empty()){ ans = 4; break; }
            swap(uv, new_uv);

            u_v.clear();
            for(auto [u,v] : uv){
                u_v.insert(u);
                u_v.insert(v);
            }
            uvvec = vector<int>(u_v.begin(), u_v.end());
            rep(i,M-1) if(0 == uv.count({ uvvec[i],uvvec[i+1] })){ ans = 5; break; }
            if(0 == uv.count({ uvvec.front(), uvvec.back() })){ ans = 5; break; }
            rep(i,M-1) uv.erase({ uvvec[i],uvvec[i+1] });
            uv.erase({ uvvec.front(), uvvec.back() });
            if(ans == 5) break;

            new_uv.clear();
            for(auto [u,v] : uv){
                int nxu = upper_bound(uvvec.begin(), uvvec.end(), u) - uvvec.begin();
                int nxv = upper_bound(uvvec.begin(), uvvec.end(), v) - uvvec.begin();
                new_uv.insert({ nxu, nxv });
            }
            if(new_uv.empty()){ ans = 4; break; }
            swap(uv, new_uv);

            if(uv.empty()){
                if(uvvec.size() % 2 == 1) ans = 5;
                else ans = 4;
            }
        }
    }
    cout << ans << endl;
    return 0;
}




struct ios_do_not_sync {
    ios_do_not_sync() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} ios_do_not_sync_instance;