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

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

char ciur[2000001]= {'0'};

int main()
{
    unsigned long long x,i,j;
   f >> x;
       for (i=2;i<=sqrt(x);i++)
    {
        if (ciur[i] == 0)
        {
       for (j=i+i;j<=x;j+=i)
        if (ciur[j] == 0) ciur[j] = 1;
       }

    }
    long k=0;
    for (i=2;i<=x;i++)
         if (ciur[i] == 0) ++k;

g << k ;
    return 0;
}