#include <stdio.h>

FILE *f,*g;

long p[2000001];

int main()
{

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

 long n,i,j,k=0;

 fscanf(f,"%ld",&n);
 fclose(f);
 for (i=1;i<=n;i++)
  p[i]=1;

 i=2;
 while(i<=n)
 {
   if(p[i]==1){
		k++;
		for(j=i+i;j<=n;j=j+i)
			p[j]=0;
	      }
   i++;
   }
 fprintf(g,"%ld",k);
 fclose(g);
 return 0;
}