c = int(input())
n = int(input())
a = [0] + list(map(int,input().split()))

dp = [10 ** 10] * (c + 1)
dp[0] = 0

for i in range(1, n + 1):
    for j in range(c + 1):
        if j + a[i] <= c:
            dp[j + a[i]] = min(dp[j + a[i]], dp[j] + 1)

if dp[c] >= 10 ** 10:
    dp[c] = -1
print(dp[c])