#include <iostream>
#include <stdio.h>

using namespace std;


FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int v[2000000],i,j,cn,n;

int main()
{
      fscanf(f,"%d",&n);
      cn=0;
      for (i=2;i<=n;i++)
           if (v[i]==0){
               cn++;
              for (j=i+i;j<=n;j=j+i)
                  v[j]=1;
                  }


       fprintf(g,"%d",cn);


     fclose(g);
	return 0;
}