l,n=map(int,input().split())
x=[0]+list(map(int,input().split()))+[l]
for i in reversed(range(1,n+2)):
  x[i]-=x[i-1]
q=[[0]*(2*l+1),[0]*(2*l+1)]
q[0][x[1]]=1
for v in x[2:]:
  nq=[[0]*(2*l+1),[0]*(2*l+1)]
  for j in range(-l,l+1):
    if q[0][j]:
      nq[0][j+v]=1
      nq[1][j-v]=1
    if q[1][j]:
      nq[0][j+v]=1
      nq[1][j-v]=1
  q=nq
g=l
for i in range(-l,l+1):
  if q[1][i]:
    g=min(g,abs(i))
print(g)