n,m = map(int, raw_input().split())
l = [int(raw_input()) for _ in range(m)]
l.sort()
mn = 50000
for i in range(m-n+1):
    a = l[i]
    b = l[i+n-1]
    if a*b < 0:
        d = min(abs(a)*2+abs(b), abs(a)+abs(b)*2)
    else:
        d = max(abs(a),abs(b))
    mn = min(mn, d)
print mn