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

INF = 100010
dp = [INF] * (C+1)
dp[0] = 0
for a in A:
    for i in range(C - a + 1):
        dp[i + a] = min(dp[i + a],dp[i] + 1)

if dp[C] == INF:
    print(-1)
else:
    print(dp[C])