#include <fstream>
#define max 2000002
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char prim[max];
long  long i,j,n,ct;
int main ()
{
    f>>n;
    for (i=2;i<=n;i++) prim[i]=1;
    for (i=2;i<=n;i++)
        if (prim[i]==1)
        {
            ct++;
            for (j=i*i;j<=n;j=j+i) prim[j]=0;
        }
    g<<ct;
}