N,M = map(int,input().split())
lsA = list(map(int,input().split()))
lsB = list(map(int,input().split()))
# Aを0,Bを1とする
lsAB = [(-10**10,0)]
for i in range(N):
    lsAB.append((lsA[i],0))
for i in range(M):
    lsAB.append((lsB[i],1))
lsAB.append((10**10,0))
lsAB.sort()
br = -10**10
ans = 0
ii = 0
while ii <= N+M:
    rs = lsAB[ii][0]
    lsBB = [rs]
    ii += 1
    while lsAB[ii][1]==1:
        lsBB.append(lsAB[ii][0])
        ii += 1
    if len(lsBB)<=1:
        continue
    lsBB.append(lsAB[ii][0])
    sm = lsBB[-1]-lsBB[0]
    maxd = 0
    for i in range(len(lsBB)-1):
        maxd = max(maxd,lsBB[i+1]-lsBB[i])
    ans += sm-maxd
print(ans)