n,m=map(int,input().split())
a,b=[],[]
for i in range(m):
    d = int(input())
    if d < 0:
        a.append(abs(d))
    else:
        b.append(d)
a.sort()
b.sort()
ans = 30000
for i in range(min(len(a),n)+1):
    aa = a[0:i]
    bb = b[0:n-len(aa)]
    if len(aa) + len(bb) != n:
        continue
    l=0 if aa == [] else max(aa)
    r=0 if bb == [] else max(bb)
    ans = min(ans, l+r+min(l,r))
print(ans)