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(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
    return x, d

N = int(input())
M = int(input())
V = []
for i in range(M):
    B,C = map(int,input().split())
    C %= B
    V.append([C,B])

x,d = remainder(V)
if x > N:
    print("NaN")
    exit(0)

for C,B in V:
    if x % B != C:
        print("NaN")
        exit(0)

print(x)