N,M=map(int,input().split())
dp=[int(input()) for i in range(M)]
dp=sorted(dp)
ans=1e10
for i in range(M-N+1):
    x=abs(dp[i])
    y=abs(dp[i+N-1])
    if dp[i+N-1]<0 or dp[i]>0 :
        ans=min(ans,max(x,y))
    else :
        ans=min(ans,x*2+y,y*2+x)
print(ans)