# include <iostream>
#include <bitset>
# include <fstream>
	
 
	
using namespace std;
	
 
	
ifstream   fin ("ciur.in");
	
ofstream fout ("ciur.out");
	
 
	
const int dim = 2000002;
	
int n, s;
bitset <2000005> E;
	
 
	
int main ()
	
 
	
{
	
        fin >> n;
	
        E[0] = 1;
	
        E[1] = 1;
	
        for ( int i = 2; i <= n; ++i)
	
            if (E[i] == 0) {
	
                ++s;
	
                for ( int j = i *i; j <= n; j += i)
	
                E[j] = 1;
	
            }
	
        fout << s;
	
return 0;
	
}