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

using namespace std;

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

short int  p[2000001];

int main()
{
    int i,n,c=0,j;
    f>>n;
    for (i=2;i<=sqrt(n);i++)
    {
        if (p[i]==0)
        {
            for (j=2*i;j<=n;j=j+i)
                p[j]=1;
        }

    }
    for (i=2;i<=n;i++)
      {
          if (p[i]==0)
            c++;
      }
      g<<c;
    return 0;
}