def main():
    l, r = map(int, input().split())

    if l == 1:
        print(0)
        exit()

    n = r-l+1

    edge = [[] for _ in range(n)]
    for i in range(l, r+1):
        x = i-l
        j = i
        while j <= r:
            y = j-l
            edge[x].append((0, y))
            edge[y].append((0, x))
            j += i
        if i != r:
            y = x+1
            edge[x].append((1, y))
            edge[y].append((1, x))

    import heapq
    def prim_heap():
        used = [True]*n
        edgelist = []
        for e in edge[0]:
            heapq.heappush(edgelist, e)
            used[0] = False
        res = 0
        while len(edgelist) != 0:
            minedge = heapq.heappop(edgelist)
            if not  used[minedge[1]]:
                continue
            v = minedge[1]
            used[v] = False
            for e in edge[v]:
                if used[e[1]]:
                    heapq.heappush(edgelist, e)
            res += minedge[0]
        return res

    print(prim_heap())

if __name__ == '__main__':
    main()