L, N = map(int, input().split())
X = list(map(int, input().split()))

dp = [False]*L*2
dp[X[0]] = True

for i in range(N-1):
  l = X[i+1] - X[i]
  ndp = [False]*L*2
  for d in range(1-L, L):
    if dp[d]: ndp[d-l] = ndp[d+l] = True
  dp = ndp

l = L - X[-1]
m = min(abs(d-l) for d in range(1-L, L) if dp[d])

print(m)