import sys
input = sys.stdin.readline
from math import gcd

def ext_gcd(a, b):
    if b==0:
        return 1, 0
    
    s, t = ext_gcd(b, a%b)
    return t, s-a//b*t

def crt(rs, ms):
    r, m = 0, 1
    
    for ri, mi in zip(rs, ms):
        if m>N:
            if r%mi!=ri%mi:
                return -1
            continue
        
        p, q = ext_gcd(m, mi)
        g = gcd(m, mi)
        
        if (ri-r)%g!=0:
            return -1
        
        r += m*(ri-r)//g*p
        m *= mi//g
        r %= m
        
        if r>N:
            return -1
    
    return r

N = int(input())
M = int(input())
BC = [tuple(map(int, input().split())) for _ in range(M)]
rs = [C for _, C in BC]
ms = [B for B, _ in BC]
ans = crt(rs, ms)

if ans>N or ans==-1:
    print('NaN')
else:
    print(ans)