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

long n,i,j,x,p;

int main(){


	FILE *fin = fopen("ciur.in", "r");
	FILE *fout = fopen("ciur.out", "w");
	fscanf(fin,"%ld", &n);


	for (i=1;i<=n;i++){
		p=1;
		for(j=1;j<=sqrt(i);j++){
			if (i%j==0)
				p=0;
		}
		if (p==1)
			x=x+1;
	}



	fprintf(fout,"x", x);
	fclose(fin);
	fclose(fout);



   return 0;
}