#include <stdio.h>
int n, i, j, nr;
char v[2000001];
int main (){
	FILE *f, *g;
	f=fopen("ciur.in","r");
	g=fopen("ciur.out","w");
	fscanf(f,"%d",&n);
	for(i=2;i<=n;i++)
	  if(v[i]==0){
      nr++;		  
	     for(j=2*i;j<=n;j=j+i)		
			 v[j]=1;
	}
fprintf(g,"%d",nr);
return 0;
}