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

sum0 = 0
D = [0] * N

def f(x):
    global sum0
    if sum0 == C:
        print(sum(D))
        exit()
    if x == N:
        return
    for i in reversed(range((C-sum0)//A[x] + 1)):
        sum0 += A[x] * i
        D[x] = i
        f(x+1)
        D[x] = 0
        sum0 -= A[x] * i

f(0)
print(-1)