#include<iostream>
#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool A[2000001];
int n;
int r = 0;
int main()
{
	fin >> n;
	for (int i = 2; i <= n; i++)
	{
		if (A[i] == 0)
		{
			r++;
			for (int j = i; j <= n;j+=i)
			{
				A[j] = 1;
			}
		}
	}
	fout << r;
}