#include<stdio.h>
long n,i,j;
char prim[2000004];
int main()
{FILE *f=fopen("ciur.in","r");
 FILE *g=fopen("ciur.out","w");



 fscanf(f,"%D",&n);
 fclose(f);
 int max=0;


 for(i=2;i<=n;i++)
    prim[i]=1;
 for (i = 2; i <= n; i++)
	  if (prim[i])
	  {
	      max++;
	      for (j = i*i; j <= n; j += i)
		  prim[j] = 0;
	  }

 fprintf(g,"%d ",max);
 fclose(f);
 return 0;
}