#include <iostream>
#include <fstream>

using namespace std;
int ciur[25005], c=0;
int main()
{
    fstream f("ciur.in"), f2("ciur.out");
    int N;
    f >> N;

    for (int j=4; j<N; j+=2){
        ciur[j]=1;
        ++c;
        }
    for (int i=3; i*i<N; i+=2)
        if (!ciur[i])
            for (int j=i*i; j<N; j+= 2*i) {
                ++c;
                ciur[j] = 1;
            }
    c=c-2;
    f2 << c;
    f.close();
    f2.close();

}