c = int(input())
n = int(input())
a = [0] + list(map(int,input().split()))

dp = [[10 ** 10] * (n + 1) for i in range(c + 1)]
for i in range(n + 1):
    dp[0][i] = 0

for i in range(1, n + 1):
    for j in range(c + 1):
        if j + a[i] <= c:
            dp[j + a[i]][i] = min(dp[j + a[i]][i], dp[j + a[i]][i-1], dp[j][i] + 1, dp[j][i - 1] + 1)

    for j in range(c + 1):
        dp[j][i] = min(dp[j][i], dp[j][i-1])

if dp[c][n] >= 10 ** 10:
    dp[c][n] = -1

print(dp[c][n])