C = int(input())
N = int(input())
A = list(map(int, input().split()))
inf = 10 ** 18
dp = [inf] * (C + 1)
dp[0] = 0
for i in range(N):
    for c in range(C + 1):
        if c - A[i] >= 0:
            dp[c] = min(dp[c], dp[c - A[i]] + 1)

print(dp[-1]) if dp[-1] != inf else print(-1)