N,M=map(int,input().split())
p=sorted([int(input()) for _ in range(M)])
m=99999
for i in range(M-N+1):
	n=p[i+N-1]
	m=min(m,n-p[i]+abs(p[i]))
	m=min(m,n-p[i]+abs(n))
print(m)