R=range
def J():
	return map(int,input().split())
L,N=J()
X=[0]+list(J())+[L]
A=[{0},set()]
E={X[1]}
for i in R(2,N+2):
	A+=[A[-1]|E]
	E={x+X[i]-X[j]for j in R(i)for x in A[j]}
print(min(abs(x*2-L)for x in A[-1]))