n,m = map(int,input().split())
A = [-10**20]+list(map(int,input().split()))+[10**20]
B = list(map(int,input().split()))
j = 0
ans = 0
for i in range(n+1):
    l,r = A[i],A[i+1]
    C = [A[i]]
    while j < m and B[j] < r:
        C.append(B[j])
        j += 1
    C.append(A[i+1])
    z = max(C[k+1]-C[k] for k in range(len(C)-1))
    ans += (C[-1]-C[0])-z
print(ans)