#include <fstream>
#define nr 2000001

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
unsigned int N, cont;
bool car[nr];
int main()
{
    in >> N;
    for(unsigned int i = 2; i <= N; ++i)
        if(!car[i])
        {
            ++cont;
            unsigned int p = 1;
            do{
                car[p * i] = 1;
                ++p;
            }while(i * p <= N);
        }
    out << cont;
    return 0;
}