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

#define MAX_N 2000001

long ciur[MAX_N],n;
int nr;


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

void compute()
{
	long i;
	for (i = 2; i <= n; i++)
	{
		if (ciur[i] == 0)
		{
			++nr;
			for (long j = i + i; j <= n; j = j + i)
			{
				ciur[j] = 1;
			}
		}
	}
}
int main()
{
	f >> n;
	compute();
	g << nr;
	f.close();
	g.close();
}