N,M = map(int,raw_input().split(" "))
D = [input() for i in range(M)] 
ans = []

for i in range(M-N+1):
    v = D[i:i+N]
    vmin = v[0]
    vmax = v[-1]
    if vmin > 0:
        ans.append(vmax)
    elif vmax < 0:
        ans.append(-vmin)
    else:
        p = abs(vmax) if (abs(vmin) > abs(vmax)) else abs(vmin)
        ans.append(abs(vmax) + abs(vmin) + p)
print min(ans)