mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N, M = map(int, input().split())
    A = list(map(int, input().split()))
    B = list(map(int, input().split()))


    A.append(10 ** 10)
    C = []
    for a in A:
        C.append((a, 0))
    for b in B:
        C.append((b, 1))
    C.sort(key=lambda x: x[0])
    ans = 0
    st = [-10 ** 10]
    for x, y in C:
        if y == 0:
            st.append(x)
            ans += st[-1] - st[0] - 1
            ma = 0
            for i in range(len(st) - 1):
                ma = max(ma, st[i+1] - st[i] - 1)
            ans -= ma
            st = [x]
        else:
            st.append(x)
    print(ans)


if __name__ == '__main__':
    main()