#include <iostream>
#include <fstream>

using namespace std;

int c[2000000];

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int n, rez;

    fin >> n;

    for(int i = 2; i * i <= n; i++){
        if(c[i] == 0){
            for(int j = i * i; j <= n; j+=i){
                c[j] = 1;
            }
        }
    }

    rez = 0;
    for(int i = 2; i <= n; i++){
        if(c[i] == 0){
            rez++;
        }
    }

    fout << rez;

    fin.close();
    fout.close();
    return 0;
}