#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int  n;
int main()
{
	int nr=1,i,j,ok;
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	for (i = 3; i <= n; i += 2){

		ok = 0;
		for (j = 2; j*j <= i;j++)
			if (i%j == 0){
				ok = 1;
				break;
			}
		if (ok == 0)
			nr++;
	}

	printf("%d", nr);
	return 0;
}