N,M=map(int,raw_input().split())
D=[int(raw_input()) for i in range(M)]
D.sort()
ans=100000
for i in range(M-N+1):
    if D[i]*D[i+N-1] >=0:
        ans=min( max(abs(D[i]),abs(D[i+N-1])), ans)
    else:
        ans=min(ans, abs(D[i]-D[i+N-1])+min(abs(D[i]),abs(D[i+N-1])) )
print ans