#include <iostream>
#include <fstream>
#include <math.h>

using namespace std;

ifstream f ("ciur.in");
ofstream g ("ciur.out");
int prim [2000000];
int main()
{
    int n,i,j,contor;
    f >>n;
    contor=0;
    for (i=2;i<=n;i++)
    {
        if (prim[i]==0)
        {
            for (j=2*i;j<=n;j=j+i)
            {
                prim[j]=1;
            }
        }
    }
    for (i=2;i<=n;i++)
    {
        if (prim[i]==0)
        {
            contor++;
        }
    }
    g <<contor;
    return 0;
}