文件目录

#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
bool ispri(int n)
{
    if (n < 2)
        return 0;
    for (int i = 2; i <= sqrt(n); i++)
        if (n % i == 0)
            return 0;
    return 1;
}
int main()
{
    int x, y;
    cin >> x >> y;
    int ans = 0;
    for (int i = x; i <= y; i++)
        if (ispri(i))
            ans++;
    cout << ans;
    return 0;
}