#include<bits/stdc++.h>
using namespace std;
//#pragma GCC optimize("Ofast")

#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
const ll dx[9]={0,1,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
ll safemod(ll a,ll m){
  return (a%m+m)%m;
}
int main(){
  ll n,m;cin >> n >> m;
  map<ll,ll> mp;
  rep(i,m){
    ll b,c;cin >> b >> c;
    c=safemod(c,b);
    if(mp.count(b)){
      if(mp[b]!=c){
        cout << "NaN" << endl;
        return 0;
      }
    }
    mp[b]=c;
  }
  for(ll i=mp.rbegin()->second;i<=n;i+=mp.rbegin()->first){
    bool ok=true;
    for(auto p:mp){
      if(i%p.first!=p.second){
        ok=false;break;
      }
    }
    if(ok){
      cout << i << endl;return 0;
    }
  }
  cout << "NaN" << endl;
}