import math

def extended_gcd(a, b):
    old_r, r = a, b
    old_s, s = 1, 0
    old_t, t = 0, 1
    while r != 0:
        quotient = old_r // r
        old_r, r = r, old_r - quotient * r
        old_s, s = s, old_s - quotient * s
        old_t, t = t, old_t - quotient * t
    return old_r, old_s, old_t

def combine(current_rem, current_mod, new_c, new_b):
    g = math.gcd(current_mod, new_b)
    if (current_rem - new_c) % g != 0:
        return None
    lcm = current_mod // g * new_b
    a = (new_c - current_rem) // g
    m_div_g = current_mod // g
    b_div_g = new_b // g
    g_inv, inv, _ = extended_gcd(m_div_g, b_div_g)
    inv %= b_div_g
    k = (a * inv) % b_div_g
    new_rem = current_rem + k * current_mod
    new_rem %= lcm
    return (new_rem, lcm)

def main():
    import sys
    input = sys.stdin.read().split()
    ptr = 0
    N = int(input[ptr])
    ptr += 1
    M = int(input[ptr])
    ptr += 1
    conditions = []
    for _ in range(M):
        b = int(input[ptr])
        c = int(input[ptr + 1])
        ptr += 2
        conditions.append((b, c))
    
    current_rem = 0
    current_mod = 1
    for b, c in conditions:
        new_b = b
        new_c = c % new_b
        res = combine(current_rem, current_mod, new_c, new_b)
        if res is None:
            print("NaN")
            return
        current_rem, current_mod = res
    if current_rem <= N:
        print(current_rem)
    else:
        print("NaN")

if __name__ == '__main__':
    main()