#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
C, N, *A = map(int, read().split())

# %%
INF = C + 100
dp = [INF] * (C + 1)
dp[0] = 0
for x in A:
    for n in range(C - x + 1):
        dp[n + x] = min(dp[n] + 1, dp[n + x])


# %%
answer = -1 if dp[C] == INF else dp[C]
print(answer)