#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

const int nMax = 2000005;

char v[nMax];

int main() {
	int n, prime = 0;
	f >> n;
	for (int i = 2; i <= n; i++)
		v[i] = 1;
	for (int i = 2; i <= n; i++) {
		if (v[i]) {
			prime++;
			for (int j = i + i; j <= n; j += i)
				v[j] = 0;
		}
	}
	g << prime;
}