#include <bits/stdc++.h>

#include <atcoder/math>
using namespace std;
using namespace atcoder;
void fast_io() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

int main() {
    fast_io();
    int n, m;
    cin >> n >> m;
    vector<long long> b(m), c(m);
    for (int i = 0; i < m; i++) {
        cin >> b[i] >> c[i];
        c[i] = (c[i] % b[i] + b[i]) % b[i];
    }
    auto [y, z] = crt(c, b);
    if (z == 0 || y > n) {
        cout << "NaN" << endl;
    } else {
        cout << y << endl;
    }
}