import sys

sys.setrecursionlimit(10 ** 6)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))

def main():
    inf=10**9
    c=II()
    n=II()
    aa=LI()
    dp=[inf]*(c+1)
    dp[0]=0
    for a in aa:
        for i in range(c+1-a):
            pre=dp[i]
            if pre==inf:continue
            if pre+1<dp[i+a]:dp[i+a]=pre+1
    if dp[c]==inf:print(-1)
    else:print(dp[c])

main()