def inv_gcd(a,b):
    a=a%b
    if a==0:
        return (b,0)
    s=b;t=a
    m0=0;m1=1
    while(t):
        u=s//t
        s-=t*u
        m0-=m1*u
        s,t=t,s
        m0,m1=m1,m0
    if m0<0:
        m0+=b//s
    return (s,m0)
def crt(r,m,nn):
    assert len(r)==len(m)
    n=len(r)
    r0=0;m0=1
    for i in range(n):
        assert 1<=m[i]
        r1=r[i]%m[i]
        m1=m[i]
        if m0<m1:
            r0,r1=r1,r0
            m0,m1=m1,m0
        if (m0%m1==0):
            if (r0%m1!=r1):
                return (0,0)
            continue
        g,im=inv_gcd(m0,m1)
        u1=m1//g
        if ((r1-r0)%g):
            return (0,0)
        x=(r1-r0)//g % u1*im%u1
        r0+=x*m0
        m0*=u1
        if r0<0:
            r0+=m0
        if r0>nn:
            return (0,0)
    return (r0,m0)

def main():
    n = int(input())
    m = int(input())
    M, R = [], []
    for _ in range(m):
        mm, rr = map(int, input().split())
        rr %= mm
        M.append(mm)
        R.append(rr)
    r, m = crt(R, M, n)
    if r == 0 and m == 0:
        print("NaN")
    else:
        print(r)

if __name__ == '__main__':
    main()