#include <iostream>
#include <fstream>
using namespace std;
ifstream I("ciur.in");
ofstream O("ciur.out");
int prim[2000000],p,n,c;

int main () {
	I>>n;
	for (int i = 2;i <= n;i ++) {
		if (!prim[i]) {
			c++;
			for (int j = 2*i;j <= n; j = j+i)
					prim[j]=1;
		}
	}
	O<<c;
}