#clean
N,M=(int(i) for i in input().split())
s=0
D=[]
nd=0
for i in range(M):
    D.append(int(input()))
    if D[i]>=0 and nd==0:
        s=i
#座標が0以上で最も原点に近い所をs
        nd=1
D.sort()
i=0
while D[i]<0:
    i+=1
s=i
i=0
mi=0
if s+N-1 <M:
    mi=D[s+N-1]
    r=0
    pl=D[s+N-1]
    mp=s+N-1
  #  print (s)
else:
    r=s+N-M
    if s-r>=0:
        mp=M-1
        pl=D[-1]
        nus=-1*D[s-r]
        if nus<pl:
            db=nus
        else:
            db=pl
        mi=pl+nus+db
    #    print (mi)
r+=1
mp-=1
while mp>=s and s-r>=0:
    nus=-1*D[s-r]
 #   print (nus)
    pl=D[mp]
 #   print (mp)
    if nus<pl:
        db=nus
    else:
        db=pl
    m1=pl+nus+db
  #  print (m1)
    if m1<mi:
        mi=m1
    r+=1
    mp-=1
if s-N>=0:
    m1=-1*D[s-N]
    if m1<mi:
        mi=m1
print(mi)