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(max(min(len(a),n),1)):
    l=0 if i < 1 else max(a[0:i])
    r=0 if n-i < 1 else max(b[0:n-i])
    ans = min(ans,  l+r+min(l,r))
print(ans)