n,m=map(int,input().split())
a=list(map(int,input().split()))
b=list(map(int,input().split()))
X=10**10
a=a+[X]
b=[-X]+b+[X]
p=[(v,1) for v in a]+[(v,0) for v in b]
p.sort()

def solve(a,r):
  if len(a)==0:
    return 0
  if len(a)==1:
    return min(a[0],r-a[0])
  return min(a[i]+r-a[i+1] for i in range(len(a)-1))

c=0
l=-X
q=[]
for v,f in p:
  if f:
    c+=solve(q,v-l)
    q=[]
    l=v
  else:
    q+=[v-l]

print(c)