from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

L,R = map(int,input().split())
class DSU:
    def __init__(self, n):
        self._n = n
        self.parent_or_size = [-1] * n

    def merge(self, a, b):
        assert 0 <= a < self._n
        assert 0 <= b < self._n
        x, y = self.leader(a), self.leader(b)
        if x == y: return x
        if -self.parent_or_size[x] < -self.parent_or_size[y]: x, y = y, x
        self.parent_or_size[x] += self.parent_or_size[y]
        self.parent_or_size[y] = x
        return x

    def same(self, a, b):
        assert 0 <= a < self._n
        assert 0 <= b < self._n
        return self.leader(a) == self.leader(b)

    def leader(self, a):
        assert 0 <= a < self._n
        if self.parent_or_size[a] < 0: return a
        self.parent_or_size[a] = self.leader(self.parent_or_size[a])
        return self.parent_or_size[a]

    def size(self, a):
        assert 0 <= a < self._n
        return -self.parent_or_size[self.leader(a)]

    def groups(self):
        leader_buf = [self.leader(i) for i in range(self._n)]
        result = [[] for _ in range(self._n)]
        for i in range(self._n): result[leader_buf[i]].append(i)
        return [r for r in result if r != []]

D = DSU(R+1)
E = []
for i in range(L,R):
    E.append((1,i,i+1))

flg = [False]*(R+1)
for i in range(L,R+1):
    if flg[i]:
        continue
    flg[i] = True
    for j in range(2*i,R+1,i):
        E.append((0,i,j))
        flg[j]=True
E.sort()
ans = 0
for w,i,j in E:
    if D.same(i,j):
        continue
    ans += w
    D.merge(i,j)
print(ans)