import sys
from functools import lru_cache

input = sys.stdin.buffer.readline

"""中国剰余定理 https://tjkendev.github.io/procon-library/python/math/chinese-remainder.html から拝借し、一部改変しています"""


@lru_cache
def extgcd(a, b):
    if b:
        d, y, x = extgcd(b, a % b)
        y -= (a // b) * x
        return d, x, y
    return a, 1, 0


# V = [(X_i, Y_i), ...]: X_i (mod Y_i)
def remainder(N, V):
    x = 0
    d = 1
    for X, Y in V:
        g, a, b = extgcd(d, Y)
        x, d = (Y * b * x + d * a * X) // g, d * (Y // g)
        x %= d
        if x > N:
            return None
        if x % Y != X:
            return None
    return x


def solve(N, V):
    res = remainder(N, V)
    if res is None:
        return "NaN"
    return res


N = int(input())
M = int(input())
V = []
for _ in range(M):
    b, c = map(int, input().split())
    c %= b
    V.append((c, b))
print(solve(N, V))