#yuki247

c=int(raw_input())
n=int(raw_input())
a=[0]+map(int,raw_input().split())
dp=[c+1]*(c+1)
dp[0]=0
for i in xrange(1,n+1):
 for j in xrange(c+1):
  if j+a[i]<=c:
   dp[j+a[i]]=min(dp[j+a[i]],dp[j]+1)
if dp[c]>=c+1:
 dp[c]=-1
print dp[c]