#include <fstream.h>
#include <stdio.h>
#include <mem.h>
#include <math.h>

FILE *f,*g;

int main()
{

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

 long long n,i,j,p[2000000],k=0;

 fscanf(f,"%lld",&n);

 memset(p,1,n);

 while(i<=sqrt(n)) if(p[i]==1) for(j=2*i;i<=n;j=j+i) p[j]=0;
			else i++;

 for(i=1;i<=n;i++) if(p[i]==1) k++;

 fprintf(g,"%lld" , k);

 fclose(f);
 fclose(g);

 return 0;

}