C = input()
N = input()
A = map(int, raw_input().split())
dp = [-1] * (10 ** 6)
dp[0] = 0
for a in A:
    for i in xrange(a, C+1):
        j = i - a
        if dp[j] < 0:
            continue
        if dp[i] < 0:
            dp[i] = dp[j] + 1
        else:
            dp[i] = min(dp[i], dp[j] + 1)
print(dp[C])