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

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


def rec(i, val):
    if i == N - 1:
        if val % A[i] == 0:
            cnt.append(val // A[i])
            return True
        return False

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


rec(0, C)
if cnt:
    print(sum(cnt))
else:
    print(-1)