def solve():
    C = int(input())
    N = int(input())
    A = list(map(int, input().split()))
    inf = float('inf')
    dp = [inf] * (C + 1)
    dp[0] = 0

    A.sort()

    for i in range(C):
        if dp[i] != inf:
            for j in range(N):
                iaj = i + A[j]
                if iaj > C:
                    break
                dp[iaj] = min(dp[iaj], dp[i] + 1)
    print(dp[C] if dp[C] != inf else -1)


if __name__ == '__main__':
    solve()