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



int n,s,ri,i,j;
char p;

int main(){
	FILE *f = fopen("ciur.in","r");
	fscanf(f,"%d",&n);
	fclose(f);
	
	s = 0;
	for (i=2;i<=n;i++) {
		
		p = 1;
		ri = (int)sqrt(i);
		
		for (j=2;j<=ri;j++)
			if (i%j == 0) {
				p = 0;
				break;
			}
		
		if (p==1)
			s++;
	}
	
	FILE *g = fopen("ciur.out","w");
	fprintf(g,"%d",s);
	fclose(g);
	
	return 0;
}