#include <iostream>
#include <stdio.h>
#include <cmath>
using namespace std;
int n;
bool a[2000000 + 100];
int main(){
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	for(int i = 2; i <= n; i++)
		a[i] = true;
	for(int i = 2; i <= sqrt((double)n); i++){
		if(a[i] == true){
			for(int j = i * i; j <= n; j += i){
				a[j] = false;
			}
		}
	}
	int c = 0;
	for(int i = 2; i <= n; i++)
		if(a[i])
			c++;

	printf("%d\n",c);
	return 0;
}