import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
# md = 10**9+7
md = 998244353

N = II()
m = II()
btoc = {}
mx = 0
for _ in range(m):
    b, c = LI()
    c %= b
    if b > mx: mx = b
    if b not in btoc:
        btoc[b] = c
    elif c != btoc[b]:
        print("NaN")
        exit()

now = []
for i in range(N+1):
    v = i*mx+btoc[mx]
    if v > N: break
    now.append(v)

for b in btoc:
    nxt = []
    c = btoc[b]
    for a in now:
        if a%b == c:
            nxt.append(a)
    now = nxt

if now:
    print(min(now))
else:
    print("NaN")