#include <iostream>
#include <fstream>
#include <vector>
#define INFILE "ciur.in"
#define OUTFILE "ciur.out"
using namespace std;

ifstream in(INFILE);
ofstream out(OUTFILE);

int main()
{
    int n;
    in>>n;
    vector<bool>Vec(n,false);
    for(int i=2;i<=n;i++){
        if(Vec[i]==false){
            for(int j=2;j*i<=n;j++){
                Vec[j*i]=true;
            }
        }
    }
    int counter=0;
    for(int i=2;i<=n;i++){
        if(Vec[i]==false)
            counter++;
    }
    out<<counter;


    return 0;
}