#include <iostream>
#include <vector>
#include<fstream>
using namespace std;
    ifstream be("ciur.in");
    ofstream ki("ciur.out");

int main()
{

    int n,db=0;
    be>>n;
    vector<bool>a(n+1,true);
    for(int i=2;i<=n;++i)
    {
        if(a[i]==true){
            db++;
            int j=2;
        while(i*j<=n)
        {
            a[i*j]=false;
            j++;
        }
        }
    }
    ki<<db;
    return 0;
}