from collections import deque

C=int(input())
N=int(input())
A=list(map(int,input().split()))
A.sort(reverse=True)

Q=deque()
Q.append((0,0,C))# 回数, index, rest

ANS=1<<31
while Q:
    s,ind,rest=Q.popleft()

    if rest==0:
        ANS=min(ANS,s)
        continue

    if ind<N:
        
        x=rest//A[ind]

        for i in range(x+1):
            Q.append((s+i,ind+1,rest-i*A[ind]))

if ANS==1<<31:
    print(-1)
else:
    print(ANS)