#include <fstream>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

bool c[2000001];

int main() {
	int n, contor = 0;
	in >> n;

	for(int i = 2; i * i <= n; i++)
		if(!c[i])
			for(int j = i * i; j <= n; j += i)
				c[j] = 1;
	
	for(int i = 2; i <= n; i++)
		if(!c[i])
			contor++;
	
	out << contor;
	
	return 0;
}