W,n,*a = map(int,open(0).read().split())
INF = 1<<60
dp = [0]+[INF]*W
for vi,wi in zip([1]*n,a):
    for x in range(wi,W+1):
        dp[x] = min(dp[x],dp[x-wi]+1)
print(dp[W] if dp[W] != INF else -1)