#include <fstream>
#include <vector>


using namespace std;


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

    int N;
    cin >> N;

    vector<bool> prim(N + 1, true);

    int result = 1;
    for(int div = 3; div <= N; div +=2)
        if(prim[div] == true){
            ++result;
        for(long long i = div * div; i <= N; i += div)
            prim[i] = false;
        }
   
    cout << result;
    
    cin.close();
    cout.close();

    return 0;
}