// -*- coding:utf-8-unix -*-
// #![feature(map_first_last)]
#![allow(dead_code)]
#![allow(unused_imports)]
#![allow(unused_macros)]
use core::num;
use std::any::Any;
use std::cmp::Ordering::*;
use std::collections::btree_map::Values;
use std::collections::*;
use std::convert::*;
use std::convert::{From, Into};
use std::error::Error;
use std::f32::consts::E;
use std::fmt::Debug;
use std::fmt::Display;
use std::fs::File;
use std::hash::Hash;
use std::io::prelude::*;
use std::io::*;
use std::iter::Filter;
use std::iter::FromIterator;
use std::marker::Copy;
use std::mem::*;
use std::ops::BitAnd;
use std::ops::Bound::*;
use std::ops::RangeBounds;
use std::ops::{Add, Mul, Neg, Sub};
use std::process;
use std::slice::from_raw_parts;
use std::str;
use std::vec;

const INF: i64 = 1223372036854775807;
const UINF: usize = INF as usize;
const LINF: i64 = 2147483647;
const INF128: i128 = 1223372036854775807000000000000;
const MOD: i64 = 1000000007;
// const MOD: i64 = 998244353;
const UMOD: usize = MOD as usize;
const M_PI: f64 = 3.14159265358979323846;
// const MOD: i64 = INF;

use std::cmp::*;
use std::collections::*;
use std::io::stdin;
use std::io::stdout;
use std::io::Write;

macro_rules! p {
    ($x:expr) => {
        println!("{}", $x);
    };
}

macro_rules! d {
    ($x:expr) => {
        println!("{:?}", $x);
    };
}
#[allow(unused_macros)]
pub mod macros {
    macro_rules! min { ($x: expr) => { $x }; ($x: expr, $($xs: expr),+) => {{ let y = macros::min!($($xs),+); std::cmp::min($x, y) } }}
    macro_rules! max { ($x: expr) => { $x }; ($x: expr, $($xs: expr),+) => {{ let y = macros::max!($($xs),+); std::cmp::max($x, y) } }}
    macro_rules! chmin { ($x: expr, $($xs: expr),+) => {{ let y = macros::min!($($xs),+); if $x > y { $x = y; true } else { false } }}}
    macro_rules! chmax { ($x: expr, $($xs: expr),+) => {{ let y = macros::max!($($xs),+); if $x < y { $x = y; true } else { false } }}}
    macro_rules! multi_vec { ($element: expr; ($len: expr, $($lens: expr),*)) => ( vec![macros::multi_vec![$element; ($($lens),*)]; $len] ); ($element: expr; ($len: expr)) => ( vec![$element; $len] ); }
    macro_rules! multi_box_array { ($element: expr; ($len: expr, $($lens: expr),*)) => ( vec![macros::multi_box_array![$element; ($($lens),*)]; $len].into_boxed_slice() ); ($element: expr; ($len: expr)) => ( vec![$element; $len].into_boxed_slice() ); }
    #[allow(unused_imports)]
    pub(super) use {chmax, chmin, max, min, multi_box_array, multi_vec};
}
fn main() {
    solve();
}

// use str::Chars;
#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn readi() -> (i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    iter.next().unwrap().parse::<i64>().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn read_mat<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn readii() -> (i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

#[allow(dead_code)]
fn readiii() -> (i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}
#[allow(dead_code)]
fn readuu() -> (usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

#[allow(dead_code)]
fn readff() -> (f64, f64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<f64>().unwrap(),
        iter.next().unwrap().parse::<f64>().unwrap(),
    )
}

fn readcc() -> (char, char) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<char>().unwrap(),
        iter.next().unwrap().parse::<char>().unwrap(),
    )
}

fn readuuu() -> (usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}
#[allow(dead_code)]
fn readiiii() -> (i64, i64, i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

#[allow(dead_code)]
fn readuuuu() -> (usize, usize, usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

pub fn gcd(a: i64, b: i64) -> i64 {
    if b == 0 {
        a
    } else {
        gcd(b, a % b)
    }
}

pub fn extgcd(a: i64, b: i64) -> (i64, i64, i64) {
    if b == 0 {
        (a, 1, 0)
    } else {
        let (gcd, x, y) = extgcd(b, a % b);
        (gcd, y, x - (a / b) * y)
    }
}
pub fn modinv(a: i64, m: i64) -> i64 {
    let (_, x, _) = extgcd(a, m);
    (m + x % m) % m
}

#[doc = "compute minimum x from a list of x = r[i] (mod m[i]) all m[i] are co-primes and some r[i] should be non-zero."]
pub fn garner(rm: Vec<(i64, i64)>, mo: i64) -> i64 {
    let mut rm = rm;
    rm.push((0, mo));
    let mut coef = vec![1; rm.len()];
    let mut constants = vec![0; rm.len()];
    for i in 0..rm.len() - 1 {
        let v = (rm[i].0 + rm[i].1 - constants[i]) * modinv(coef[i], rm[i].1) % rm[i].1;
        for j in i + 1..rm.len() {
            constants[j] += coef[j] * v;
            constants[j] %= rm[j].1;
            coef[j] *= rm[i].1;
            coef[j] %= rm[j].1;
        }
    }
    constants[rm.len() - 1]
}
#[doc = "none if there is no such x"]
pub fn pre_garner(rm: &mut Vec<(i64, i64)>, mo: i64) -> Option<i64> {
    let n = rm.len();
    for i in 0..n {
        for j in 0..i {
            let g = gcd(rm[i].1, rm[j].1);
            if (rm[i].0 - rm[j].0) % g != 0 {
                return None;
            }
            rm[i].1 /= g;
            rm[j].1 /= g;
            let mut gi = gcd(rm[i].1, g);
            let mut gj = g / gi;
            loop {
                let g = gcd(gi, gj);
                gi *= g;
                gj /= g;
                if g == 1 {
                    break;
                }
            }
            rm[i].1 *= gi;
            rm[j].1 *= gj;
            rm[i].0 %= rm[i].1;
            rm[j].0 %= rm[j].1;
        }
    }
    let mut lcm = 1;
    for i in 0..n {
        lcm = lcm * rm[i].1 % mo;
    }
    Some(lcm)
}

fn solve() {
    let n: usize = read();
    let m: usize = read();
    let mut data = vec![];
    let mut st = BTreeSet::new();
    for i in 0..m {
        let (b, c) = readii();
        if !st.contains(&((c % b + b) % b, b)) {
            data.push(((c % b + b) % b, b));
        }
        let last_data = *data.last().unwrap();
        st.insert(last_data);
    }
    let mut d1 = data.clone();
    let mut d2 = data.clone();
    let mut y1 = pre_garner(&mut d1, 101737);
    if y1.is_none() {
        p!("NaN");
        return;
    }
    let y2 = pre_garner(&mut d2, 101741);
    if y1 != y2 {
        p!("NaN");
        return;
    }
    if y2.is_none() {
        p!("NaN");
        return;
    }
    // x が答え
    let mut x1 = garner(d1, 101737);
    let mut x2 = garner(d2, 101741);
    if x1 != x2 {
        p!("NaN");
        return;
    }
    let mut x = x1;
    if x > n as i64 {
        p!("NaN");
        return;
    }
    p!(x);
    // d!(x);

    return;
}