#include <fstream>
#include <cmath>

int main(void)
{
    std::ifstream in("ciur.in");
    int nV, nA(0);
    in >> nV;
    in.close();
    nV++;
    bool *bCh = new bool[nV];
    for(int i(0); i < nV; i++)
        bCh[i] = true;
    for(int i(2); i < sqrt(nV); i++)
        if(bCh[i])
            for(int j(i * i); j < nV; j += i)
                bCh[j] = false;
    std::ofstream out("ciur.out");
    for(int i(2); i < nV; i++)
        if(bCh[i]) nA++;
    out << nA;
    delete[] bCh;
    out.close();
    return 0;
}