import sys
input = lambda: sys.stdin.readline().strip()

def Map():
  return list(map(int,input().split()))

L,N = Map()
X = Map()
W = []
for i in range(N-1):
  d = X[i+1] - X[i]
  W.append(d)

dp = [0 for i in range(L+1)]
dp[0] = 1
for w in W:
  for l in range(L,-1,-1):
    if dp[l]:
      ll = l + w
      if ll <= L:
        dp[ll] = 1

ans = L
for l in range(L):
  if dp[l]:
    a = l + X[0]
    b = L - a
    ans = min(ans,abs(a-b))
print(ans)