from collections import *
from itertools import *
from functools import *
from heapq import *
import math,sys
input = sys.stdin.readline

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

INF = (1<<60)
dp = [INF]*(C+2)

dp[0] = 0
for a in A:
    
    for i in range(C):
        
        dp[min(C+1,i+a)] = min(dp[min(C+1,i+a)],dp[i]+1)
        
if dp[C]==INF:
    print(-1)
else:
    print(dp[C])