import sys

input = sys.stdin.buffer.readline


def solve(N, M, V):
    MAX = 10 ** 5
    mod_table = [None] * (MAX + 1)
    for c, b in V:
        if mod_table[b] is None:
            mod_table[b] = c
        elif mod_table[b] != c:
            return "NaN"
    res_table = [0] * (N + 1)
    for i, mod in enumerate(mod_table):
        if mod is None:
            continue
        for x in range(mod, N + 1, i):
            res_table[x] += 1
    for i in range(N + 1):
        if res_table[i] == M:
            return i
    return "NaN"


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, M, V))