#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
short int prim[20000000];
int main()
{
    int n,i,x,d,contor,j;
    contor=0;
    f>>n;
    for (i=2;i<=sqrt(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;
}