inf = 10**9
C = int(input())
N = int(input())
A = list(map(int, input().split()))

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])