def f(a,b):
    if b<=0:
        return -a
    elif a<=0<=b:
        return min(b-2*a,2*b-a)
    else:
        return b

N,M=map(int,input().split())
D=[]
for i in range(M):
    D.append(int(input()))

D.sort()

E=[]
for k in range(M-N+1):
    E.append(f(D[k],D[k+N-1]))

print(min(E))