#include <iostream>
#include <fstream>
using namespace std;

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

char vector[2000005];

int main()
{
	int n;
	f >> n;
	
	int  i, j, nr = 1;

	for (i = 3; i <= n; i += 2)
	{
		if (vector[i] == 0)
		{
			nr++;
			for (j = i + i + i; j <= n; j += i << 1)
			{
				vector[j] = 1;
			}
		}
	}
	
	g << nr;
}