#include <stdio.h>
#include <fstream>
#include <math.h>
#define lim 2000000
using namespace std;

bool v[lim];

int main() {
	int n, i, nr = 1;
	long long j;
	
	ifstream in("ciur.in");
	ofstream out("ciur.out");
	
	in >> n;
	for (i = 3; i <= n; i = i + 2)
		if (v[i] == false)
			for (j = (long long)i * i; j <= n; j = j + i)
				v[j] = true;
	for (i = 3; i <= n; i = i + 2) {
		//out << v[i] << ' ';
		if (v[i] == false)
			nr++;
	}
	out << nr << '\n';

	in.close();
	out.close();
	return 0;
}