#include <cstdio>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <cmath>
#define rep(i,a,n) for(int i=a;i<n;i++)
using namespace std;

int main(void){
	int i,j,k,n,a=1;
	cin >> n;
	if(n==1){
		cout << "0\n";
		return 0;
	}
	for(i=3;i<=n;i+=2){
		k=0;
		for(j=3;j<=sqrt(i);j+=2){
			if(i%j==0){
				k=1;
				break;
			}
		}

		if(k==0) a++;
	}

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