#include <iostream>
#include <cstdio>


using namespace std;

FILE *f,*g;

int main()
{
 f=fopen("ciur.in","r");
 g=fopen("ciur.out","w");
 long n,i,nr=0;
 char A[2000001];
 fscanf(f,"%d",&n);
 for(i=1;i<=n;i++)
 {
     A[i]=0;
 }
 int k,p=2;
 while(p<=n)
 {
     if(A[p]==0)
     {
         nr++;
         k=p+p;
         while(k<=n)
         {
             A[k]=1;
             k=k+p;
         }
     }
     p++;
 }
 fprintf(g,"%d\n",nr);
 return 0;
}