#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
long long gcd(long long a, long long b) {
	if (b == 0) return a;
	else return gcd(b, a%b);
}

long long lcm(long long x, long long y) {
	return x * y / gcd(x, y);
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, m; cin >> n >> m;
	vector<long long>b(m), c(m);
	rep(i, m)cin >> b[i] >> c[i];
	rep(i, n + 1) {
		bool chk = true;
		rep(j, m) {
			if (0 != (i - c[j]) % b[j]) {
				chk = false;
				break;
			}
		}
		if (chk) {
			cout << i << endl;
			return 0;
		}
	}
	cout << "NaN" << endl;
	return 0;
}