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

int v[2000002];


int main ()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n,i,j,contor;
    f>>n;
    for (i=2; i<=n; i++)
    {
        if (v[i]==0)
        {
            for (j=2; j*i<=n; j++)
                v[i*j]=1;
        }
    }
    contor=0;
    for (i=2; i<=n; i++)
    {
        if (v[i]==0)
            contor++;
    }
    g<<contor<<endl;
}