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