文件目录

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int a, b;
    cin >> a >> b;
    int c = 0;
    for (int i = a; i <= b; i++)
    {
        int n = i;
        bool f = true;
        for (int j = 2; j <= sqrt(n); j++)
        {
            if (n % j == 0)
            {
                f = false;
                break;
            }
        }
        if (f)
            c++;
    }
    cout << c;
    return 0;
}