#include <iostream>
#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

const int NMax = 2e6 + 5;

int N;
bool notPrime[NMax];

int main() {
    in>>N;

    int nr = 1;
    for (int i=3;i<=N;i+=2) {
        if (notPrime[i]) {
            continue;
        }

        ++nr;
        for (int j=3*i;j<=N;j+=2*i) {
            notPrime[j] = true;
        }
    }

    out<<nr<<'\n';

    in.close();out.close();
    return 0;
}