#include <fstream>
#include <iostream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
	int n;
    f >> n;
    bool nonprim[2000001];
    nonprim[1] = 1;
    nonprim[2] = 0;
	int nrprim = 0;
	int i, j;
    for (i=2; i<=n; i++)
	{
		if (!nonprim[i])
		{
			nrprim++;
			for (j=i; j<=n; j+=i)
			{
				nonprim[j] = 1;
			}
		}
	}
	g << nrprim;
}