#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 rep(t,1){
        set<pair<int,int>> uv;
        set<int> u_v;
        rep(i,M){
            int u,v; cin >> u >> v; u--; v--;
            uv.insert(make_pair(u,v));
            u_v.insert(u);
            u_v.insert(v);
        }
        vector<int> uvvec(u_v.begin(), u_v.end());
        if(M != uvvec.size()){ ans = 5; break; }
        rep(i,M-1) if(0 == uv.count({ uvvec[i],uvvec[i+1] })){ ans = 5; break; }
        if(!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; }
    }
    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;