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

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

int n, nr;
bool  p[2000001];

int main()
{
	fin >> n;
	fin.close();
	int i, j;
	i = 2;
	nr = 0;
	do 
	{
		if (p[i] == 0)
		{
			nr++;
			for (j = i * i; j <= n; j += i)
				p[j] = 1;
		}
		i ++;
	}
	while ( i <= n);
	fout << nr << '\n';
	fout.close();
	return 0;
}