c,n=int(input()),int(input())
a=list(map(int,input().split()))
dp=[1<<30]*(c+1);dp[0]=0
for i in range(c):
    if dp[i]==1<<30:
        continue
    for j in a:
        if i+j<=c:
            dp[i+j]=min(dp[i+j],dp[i]+1)
if dp[-1]==1<<30:
    print(-1)
else:
    print(dp[-1])