#include <stdio.h>
#include <math.h>
FILE *in,*out;
int N,c[2000001],cnt,i,j;
using namespace std;
int main()
{
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");
    fscanf(in,"%d",&N);
    for(i=2;i<=N; i++)
         c[i]=1;
    for(i=2;i<=N;i++)
	  if (c[i])
	   {
	   ++cnt;
		   for (j=i+i; j<=N; j+=i)
			   c[j]=0;
	   }
    fprintf(out,"%d", cnt);
    fclose(in);
    fclose(out);
    return 0;
}