#include <bits/stdc++.h>
#define ll long long
using namespace std;


ifstream fin("ciur.in");
ofstream fout("ciur.out");


bool v[2000005];

int main(){
	ll n;
	fin>>n;

	int counter = 1;

	for(int i = 3; i <= n; i+=2) {
		if(!v[i]) {
			counter++;
			v[i] = 1;
			for(int j = i+i; j <= n; j+=i){
				v[j] = 1;
			}
		}
	}

	fout<<counter;

}