#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001
long long N,M;


int main(){
	
	cin>>N>>M;
	vector<long long> r,m;
	map<long long,long long> mp;
	rep(i,M){
		long long b,c;
		cin>>b>>c;
		
		c += b * 10000;
		c %= b;
		if(mp.count(b)){
			if(mp[b]!=c){
				cout<<"NaN"<<endl;
				return 0;
			}
		}
		mp[b] = c;
	}
	
	vector<pair<long long,long long>> rs;
	for(auto a:mp){
		rs.emplace_back(a.first,a.second);
	}
	reverse(rs.begin(),rs.end());
	for(long long i=0;i<=N;i++){
		bool f = true;
		rep(j,rs.size()){
			if(i%rs[j].first!=rs[j].second){
				f = false;
				break;
			}
		}
		if(f){
			cout<<i<<endl;
			return 0;
		}
		
	}
	cout<<"NaN"<<endl;
	
	return 0;
}