#include<fstream>
#include<iostream>
using namespace std;
bool prim[2100100];
int n;
int ciur() {
	int i,j,cont=1;
	for(i=3;i<=n;i+=2)
		if(!prim[i]) {
			cont++;
			for (j = i + i + i; j <= n; j += i << 1)
				prim[j]=1;
		}
	return cont;
}
int main() {
	long long clo=clock();
	ifstream in("ciur.in");
	in>>n;
	in.close();
	ofstream out("ciur.out");
	out<<ciur()<<'\n';
	out.close();
	cout<<clock()-clo<<" ms";
	return 0;
}