#include <iostream>
#include <fstream>
#include <cmath>
 
#define MAX 2000001
 
using namespace std;
 
ifstream inf("ciur.in");
ofstream outf("ciur.out");
 
bool e_multiplu[MAX];

int main()
{
    int n, nr = 0; inf >> n;
    
    for(int i = 2; i <= n; i++)
    {
        if(e_multiplu[i]) continue;
        
        for(int j = i * i; j <= n; j += i)
        {
            e_multiplu[j] = true;
        }
        
        nr++;
    }
    
    outf << nr;
}