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

int n;
bool v[2000000];
int i = 0,j=0,p=0,nr = 0;
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()

{
    in>>n;
    for(i=2;i<=n;i++){
        if(v[i] != 1){
            for(j=2*i;j<=n;j+=i){
                v[j] = 1;
            }
            nr++;
        }
    }
    out<<nr;

}