#include <stdio.h>
main(){
	FILE *f,*g;
	int a[100000];
	int ok,n,k,i,nr,j;
	f=fopen("ciur.in","r");
	g=fopen("ciur.out","w");
	fscanf(f,"%d",&n);
	k=0;
	ok=0;
	i=1;
	nr=0;
	while (i<n-1) {
		if(i<3)
			i=i+2; else i++;
		ok=0;
		for(j=1;j<=k;j++)
		if (i %a[j]==0){
			ok=1;
			break;
			}
			
		if (ok==0){
         k++;
		 a[k]=i;
		 nr++;
		}			
		
			
			
		}
		
		
		
		
		fprintf(g,"%d",nr);
		fclose(g);
	
		return 0;
	}