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

INF = 100010
dp = [INF] * (C+1)
dp[0] = 0
for a in A:
    for i in range(1, C//a + 1):
        for j in reversed(range(C - a * i + 1)):
            dp[j + a * i] = min(dp[j + a * i],dp[j] + i)
if dp[C] == INF:
    print(-1)
else:
    print(dp[C])