#include <fstream>
#include <cstring>

#define DN 2000005
using namespace std;

bool prim[DN];

int main() {
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    int n, rez=0;
    memset(prim,1, sizeof(prim));
    f>>n;
    for (int i=2; i<=n ; ++i) {
        if (prim[i] == true) {
            ++rez;
            for (int j=i; j<=n ; j+=i)
                prim[j] = false;
        }
    }
    g<<rez;
    return 0;
}