C = int(raw_input())
N = int(raw_input())
a = map(int,raw_input().split(" "))
UB = 10**5+1
dp = [[UB for i in range(C+1)] for i in range(N+1)]

for i in range(N):
	dp[i][0] = 0
	for j in range(a[i],C+1):
		if dp[i][j-a[i]] + 1 < dp[i][j]:
			dp[i][j] = dp[i][j-a[i]] + 1
	for j in range(C+1):
		dp[i+1][j] = dp[i][j]

if dp[N-1][C] == UB:
	print -1
else:
	print dp[N-1][C]