def read_data():
    C = int(input())
    N = int(input())
    As = list(map(int, input().split()))
    return C, N, As

def solve(C, N, As):
    As.sort()
    lower, residue = divmod(C, As[-1])
    if residue == 0:
        return lower
    lower += 1
    upper = C // As[0]
    for total in range(lower, upper + 1):
        if has_solution(total, C, As, N-1):
            return total
    return -1

def has_solution(total, C, As, idx):
    a = As[idx]
    if idx == 0:
        n, r = divmod(C, a)
        return r == 0 and n == total
    for n in range(C//a, -1, -1):
        new_total = total - n
        new_C = C - n * a
        if new_C > new_total * As[idx - 1]:
            return False
        result = has_solution(new_total, new_C, As, idx - 1)
        if result:
            return True
    return False

C, N, As = read_data()
print(solve(C, N, As))