#include <iostream>
#include <fstream>
#include <vector>

int main() {
    std::ifstream fileIn("ciur.in");
    std::ofstream fileOut("ciur.out");

    int nV, nCount;

    fileIn >> nV;

    nV++;

    std::vector<bool> check(nV, true);

    check[2] = true;
    for (int i(2); i < nV; i++) {
        if (check[i]) {
            nCount++;
            for (int j(i + i); j < nV; j += i) {
                check[j] = false;
            }
        }
    }

    fileOut << nCount;

    fileIn.close();
    fileOut.close();

    return 0;
}