C++ :

#include <iostream>
#include "bit"
#include "vector"
#include "unordered_set"
#include "set"
#include "queue"
#include "algorithm"
#include "bitset"

using namespace std;

/*
如果一个正整数的最大质因子不超过 B，则该正整数为 B-smooth 数。小杨同学想知道，对于给定的 n 和 B，有多少个不超过 n 的 B-smooth 数。
1 if x <= B then x is a B-smooth number
2 if x > B && x is prime number, then x is not a  B-smooth  number
3 if x > B && x is product of prime number, then x is not a B-smooth  number
 */

const int N = 1e6 + 1;
bitset<N> s, t;
int p[N], n, B, x = 0;

int main() {
    cin >> n >> B;
    if (n <= B) {
        cout << n;
        return 0;
    }

    for (int i = 2; i <= n; i++) {
        if (!s.test(i)) p[x++] = i;
        for (int j = 0; j < x && p[j] * i <= n; j++) {
            s.set(p[j] * i);
            if (i % p[j] == 0) break;
        }
    }

    int y = upper_bound(p, p + x, B) - p;

    for (; y < x; y++) {
        for (int i = 1; p[y] * i <= n; i++) {
            t.set(p[y] * i);
            //if(i % p[y] == 0) break;
        }
    }

    int sum = 0;
    for(int i = B + 1; i <= n; i++){
        if(t.test(i)) sum++;
    }

    cout << n - sum;

}