N, S = map(int,input().split())
if S > 0:
l = [*map(int,input().split())]
else:
l = []
L = [i for i in range(1,1005) if i not in l]
ans = 9876543210
for i in L:
if i in l or (i - N > ans):
continue
for j in L:
if j in l or i*j - N > ans:
continue
for k in L:
if k in l:
continue
ans = min(ans, abs(N - i*j*k))
if N < i*j*k:
break
print(ans)