//Enunt: https://www.infoarena.ro/problema/ciur
#include <iostream>
#include <fstream>
#define len 2000001
#define fin "ciur.in"
#define fout "ciur.out"

using namespace std;
ifstream in(fin);
ofstream out(fout);
int n, cont;
bool ciur[len];
int main()
{
    in >> n;
    for(int d = 2; d <= n; ++d)
        if(!ciur[d])
        {
            ++cont;
            int k = 2;
            while(d * k <= n)
            {
                ciur[d * k] = 1;
                ++k;
            }
        }
    out << cont;
    return 0;
}