N, M = map(int, input().split())
D = [int(input()) for _ in range(M)]
D += [0, -float('inf'), float('inf')]
D.sort()
for i in range(M+2):
    if D[i] == 0:
        l = i
        r = i
        break
    
ans = 0
cnt = 0
while cnt < N:
    dmx, dmn= max(abs(D[l-1]), abs(D[r])), min(abs(D[l-1]), abs(D[r]))
    lx = dmn*2 + dmx
    dmx, dmn= max(abs(D[l]), abs(D[r+1])), min(abs(D[l]), abs(D[r+1]))
    rx = dmn*2 + dmx
    if lx > rx:
        ans = rx
        r += 1
    else:
        ans = lx
        l -= 1
    cnt += 1
print(ans)