#include <fstream>
#include <bitset>
#define limit 2000000

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int n, k;
bitset <limit + 1> e;

void ciur(){

    for(int i = 1; i <= n; i++)
        e[i] = 1;
}


int main(){

    cin >> n;
    ciur();

    for(int i = 2; i <= n; i++){
        if(e[i]){

            k++;

            for(int d = i; d <= n; d += i)
                e[d] = 0;
        }
    }

    cout << k;

}