def solve():
    N=int(input())
    M=int(input())

    B=[0]*M; C=[0]*M
    for i in range(M):
        B[i],C[i]=map(int,input().split())
        C[i]%=B[i]

    B_max=max(B)
    A=[-1]*(B_max+1)
    K=0
    for i in range(M):
        if A[B[i]]>=0 and A[B[i]]!=C[i]:
            return "NaN"
        if A[B[i]]==-1:
            A[B[i]]=C[i]
            K+=1

    X=[0]*(N+1)
    for b in range(1,B_max+1):
        if A[b]==-1:
            continue

        for k in range(A[b],N+1,b):
            X[k]+=1

    for n in range(N+1):
        if X[n]==K:
            return n
    else:
        return "NaN"
#==================================================
print(solve())