#include <iostream>
#include <fstream>
using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");

int n, a[2000001], i, j, k;

int main()
{
    f >> n;
    a[1] = 1;

    for (i=4; i<=n; i=i+2)
        a[i] = 1;

    for (i=2; i*i<=n; i++)
        if (a[i]==0)
            for (j=2; j*i<=n; j++)
                a[j*i] = 1;

    for (i=1; i<=n; i++)
        if (a[i]==0)
            k++;

    g << k;
}