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

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

    bool a[2000000];

int main()
{
    int i,n,j,counter = 0;
    f>>n;

    for(i = 2;i <= n;i++)
    {
        if(!a[i])
        {
            counter++;
            for(j = i * 2;j <= n;j += i)
                a[j] = 1;
        }
    }

    g<<counter;
    return 0;
}