#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N,nr;
bool prim[2000002];
int main()
{
    f>>N;
    for (int i = 2; i <= N; ++i)
        prim[i] = 1;
    for (int i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++nr;
            for (int j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
     g<<nr<<' ';
    return 0;
}