#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
        nd=1
i=0
mi=0
if s+N-1 <len(D):
    mi=D[s+N-1]
    r=0
    pl=D[s+N-1]
    mp=s+N
  #  print (s)
else:
    r=s+N-len(D)+1
    if s-r>=0:
        mp=len(D)-1
        pl=D[-1]
        nus=D[s-r]*-1
        if nus<pl:
            db=nus
        else:
            db=pl
        mi=pl+nus+db
r+=1
while s-r>=0:
    nus=-1*D[s-r]
    mp-=1
    pl=D[mp]
    if nus<pl:
        db=nus
    else:
        db=pl
    m1=pl+nus+db
    if m1<mi:
        mi=m1
    r+=1
print(mi)