C = int(input())
n = int(input())
A = list(map(int, input().split()))
dp = [1 << 30] * (C + 1)
dp[0] = 0
for a in A:
    for i in range(a, C + 1):
        dp[i] = min(dp[i], dp[i - a] + 1)
ans = dp[-1]
if ans == 1 << 30:
    ans = -1
print(ans)