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