#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int,int>
#define pil pair<int,ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int,int>>
#define vpll vector<pair<ll,ll>>
#define vvpii vector<vector<pair<int,int>>>
#define vvpll vector<vector<pair<ll,ll>>>

template<typename T> void debug(T e){
    cerr << e << endl;
}

template<typename T> void debug(vector<T> &v){
    rep(i, v.size()){
        cerr << v[i] << " ";
    }
    cerr << endl;
}

template<typename T> void debug(vector<vector<T>> &v){
    rep(i, v.size()){
        rep(j, v[i].size()){
            cerr << v[i][j] << " ";
        }
        cerr << endl;
    }
}

template<typename T> void debug(vector<pair<T, T>> &v){
    rep(i,v.size()){
        cerr << v[i].first << " " << v[i].second << endl;
    }
}

template<typename T> void debug(set<T> &st){
    for (auto itr = st.begin(); itr != st.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(multiset<T> &ms){
    for (auto itr = ms.begin(); itr != ms.end(); itr++){
        cerr << *itr << " ";
    }
    cerr << endl;
}

template<typename T> void debug(map<T, T> &mp){
    for (auto itr = mp.begin(); itr != mp.end(); itr++){
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out(){
    cerr << endl;
}

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T){
    cerr << H << " ";
    debug_out(T...);
}

int main(){
    ll N;
    cin >> N;
    ll M;
    cin >> M;
    vector<ll> B(M);
    vector<ll> C(M);
    rep(i,M){
        cin >> B[i] >> C[i];
    }
    rep(i,M){
        C[i] = (C[i] + B[i] * 1000000) % B[i];
    }

    vector<pll> p(M);
    rep(i,M){
        p[i].first = B[i];
        p[i].second = C[i];
    }
    sort(all(p));
    
    vector<ll> counter(N + 2, 0);
    ll cnt = 0;

    for (ll i = p[0].second; i < N + 2; i += p[0].first){
        counter[i]++;
    }
    cnt++;
    bool pos = true;
    for (ll i = 1; i < M; i++){
        if (p[i].first == p[i - 1].first){
            if (p[i].second != p[i - 1].second){
                pos = false;
                break;
            }
        }
        else{
            cnt++;
            for (ll j = p[i].second; j < N + 2; j += p[i].first){
                counter[j]++;
            }
        }
    }

    if (!pos){
        cout << "NaN" << endl;
    }
    else{
        for (ll i = 0; i <= N; i++){
            if (counter[i] == cnt){
                cout << i << endl;
                return 0;
            }
        }
        cout << "NaN" << endl;
    }
}