N, M = map(int, input().split())
D = [int(input()) for _ in range(M)]
D.sort()
ans = 10**18

for i in range(M-N+1):
    j = i+N-1
    
    if D[i]<0 and D[j]<0:
        ans = min(ans, -D[i])
    elif D[i]<0 and D[j]>=0:
        ans = min(ans, -2*D[i]+D[j], 2*D[j]-D[i])
    else:
        ans = min(ans, D[j])

print(ans)