#include <stdio.h>
 
using namespace std;
 
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
 
int i,j,N,k;
bool v[2000000];
 
int main()
{
    fscanf(f,"%d",&N);
    for(i=3;i<=N;i+=2)
     if(v[i]==0)
      {
         for(j=3*i;j<=N;j+=2*i)
          v[j]=1;
         k++;
      }
    fprintf(g,"%d",k+1);
    fclose(g);
    return 0;
}