#include<iostream>
#include<fstream>
using namespace std;
char prim[ 2000005];
 unsigned short nr=0,n;
int main ()
{
    ifstream x("ciur.in");
    ofstream y("ciur.out");
    ;
    unsigned short i,j;
    x>>n;
    for(i=2;i<=n;i++)
    prim[i]=1;
    for(i=2;i<=n;i++)
    {
        if(prim[i]!=0)
        {
            nr++;
            for(j=i+1;j<=n;j+=i)
            prim[j]=0;
        }
    }
    y<<nr;
    x.close();
    y.close();
    return 0;
}