#include <iostream>
using namespace std;

int countPrimes(int n) 
{
    int count = 0;
    for (int num = 2; num <= n; ++num) 
    {
        bool isPrime = true;
        for (int i = 2; i * i <= num; ++i) 
        {
            if (num % i == 0) 
            {
                isPrime = false;
                break;
            }
        }
        if (isPrime) 
        {
            count++;
        }
    }
    return count;
}

int main() {
    int n;
    cin >> n;

    cout << countPrimes(n) << endl;

    return 0;
}