#include <fstream>
#include <iostream>

using namespace std;

int main(){

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

    int N, s = 0;
    fin >> N;

    int primes[N + 1] = {1};
    for(int i = 0; i <= N; ++i){
        primes[i] = 1;
    }
    primes[0] = 0;
    primes[1] = 0;

    for(int i = 2; i <= N; ++i){
        if(primes[i]){
            for(int j = 2; j * i <= N; ++j){
                primes[j * i] = 0;
            }
            s++;
        }
    }

    fout << s << "\n";

    return 0;
}