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

DP=[1<<31]*(C+1)
DP[C]=0

for i in range(C,-1,-1):
    for a in A:
        if i>=a:
            DP[i-a]=min(DP[i-a],DP[i]+1)

if DP[0]==1<<31:
    print(-1)
else:
    print(DP[0])