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

dp = [10**10] * (C+1)
dp[0] = 0

for i in range(N):
    for j in range(C):
        if j+A[i] <= C:
            dp[j+A[i]] = min(dp[j+A[i]], dp[j]+1)

if dp[C] == 10**10:
    print(-1)
else:
    print(dp[C])