#include <iostream>

using namespace std;

int main() {
    int a, b;
    while (cin >> a >> b) {
        int min, max, sum=0;
        if (a > b) {
            min = b;
            max = a;
        } else {
            min = a;
            max = b;
        }
        int arr[max+1];
        for (int i = 0; i <= max; i++)//初始化一个全为1的数组
            arr[i] = 1;
        for (int i = 2; i <= max; i++) {//素数的倍数一定不是素数
            if (arr[i] == 1) {
                for (int j = i; j <= max; j += i) {
                    arr[j] = 0;
                }
                arr[i] = 1;
            }
        }
        for (int i = min; i <= max; i++) {
            if (arr[i] == 1)
                sum++;
        }
        cout << sum << endl;
    }
    return 0;
}