#include <iostream>
#include <fstream.h>

bool v[2000001];

int main()
{
	ifstream f ("ciur.in");
	ofstream g ("ciur.out");
	
	int i, j, n, contor = 0;
	
	f >> n;
	
	for (i = 2; i <= n; i ++)
		if (!v[i])
			for (j = i * 2; j <= n; j += i)
				v[j] = true;
	
	for (i = 2; i <= n; i ++)
		if (!v[i])
			contor ++;
		
	g << contor;
	
	f.close();
	g.close();
}