#include <iostream>
#include <fstream>

#define MAX_N 2000005
using namespace std;


long countPrimes(long n) {
	bool sieve[MAX_N];

	int count = 0;
	for (long i = 0; i<n; i++)
		sieve[i] = true;

	for (long i = 2; i<n; i++) {
		if (sieve[i] == true) {
			for (long index = i+i; index < n; index+=i) {
				sieve[index] = false;
			}
			count++;
		}
	}
	
	return count;
}

int main() {
	ifstream f("ciur.in");
    ofstream g("ciur.out");
    long n;
    f>>n;
	g<<countPrimes(n);
	return 0;
}