#include <iostream>
#include <fstream>

using namespace std;

int main()
{
	long n, i, j, c = 0;
	
	ifstream infile ("ciur.in");
	ofstream outfile ("ciur.out");
	
	infile >> n;
	bool v[n];
	for (i = 0; i <= n; i++)
	{
		v[i] = 1;
	}
	
	for (i = 2; i <= n; i++)
	{
		if (v[i] == 1)
		{	
			c ++;
			for (j = i * 2; j <= n; j += i)
				v[j] = 0;
		}
	}
	
	outfile << c;
	outfile.close();
}