import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)
inf = 10**18

C = int(input())
N = int(input())
A = list(map(int, input().split()))
A.sort(reverse=True)
cnt = []
ans = inf


def rec(i, val):
    global ans
    if i == N:
        if val == 0:
            ans = min(ans, sum(cnt))
        return

    x_max = val // A[i]
    for x in reversed(range(x_max + 1)):
        cnt.append(x)
        rec(i + 1, val - A[i] * x)
        cnt.pop()


rec(0, C)
if ans >= inf:
    ans = -1

print(ans)