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

long n,i,j,k,p,x,d;
char a[2000002];

int main(){


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


	for (i=2;i<=n;i++)
	  if (a[i]==0)
	    for (j=i+i;j<=n;j=j+i)
	      a[j]=1;


	for (i=2;i<=n;i++){
		if (a[i]==0)
			x=x+1;
	}




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



   return 0;
}