/*
 * main.c
 *
 *  Created on: Jun 9, 2015
 *      Author: Admin
 */
#include<stdio.h>
#include<stdlib.h>

int main(void)
{
	int a[200000]={0};
	int i,j;
	int N,nr=0;

	FILE *in;
	FILE *out;

	in=fopen("ciur.in","r");
	out=fopen("ciur.out","w");

	fscanf(in,"%d", &N);
	a[0]=1;a[1]=1;

	for(i=2;i<N;++i)
	{
		if(a[i]==0)
		{
			++nr;
			for(j=i+i;j<=N;j+=i)
			{
				a[j]=1;
			}
		}

	}



	fprintf(out,"%d", nr);

	fclose(in);
	fclose(out);

	return 0;

}