n=int(input())
m=int(input())
M=10**5+10
bc=[-1]*M
cnt=0
for i in range(m):
  b,c=map(int,input().split())
  c%=b
  if bc[b]==-1:
    bc[b]=c
    cnt+=1
  else:
    if bc[b]!=c:
      print('NaN')
      exit()

ok=[0]*(n+1)
for i in range(M):
  if bc[i]!=-1:
    tmp=bc[i]
    while tmp<=n:
      ok[tmp]+=1
      tmp+=i

for i in range(n+1):
  if ok[i]==cnt:
    print(i)
    exit()

print('NaN')