#include <iostream>
#include <fstream>
using namespace std;
int k;
bool viz[2000005];
void ciur(int n)
{
    k = 1;
    for (int i = 4; i <= n; i = i + 2)
    {
        viz[i] = 1;
    }
    for (int i = 3; i <= n; i = i + 2)
    {
        if(viz[i] == 0)
        {
            k++;
            for (int j = 3 * i; j <= n; j = j + (2 * i))
            {
                viz[j] = 1;
            }
        }
    }
}
int main()
{
    int n;
    ifstream f ("ciur.in");
    ofstream g ("ciur.out");
    f >> n;
    ciur(n);
    g << k;
    return 0;
}