#include <fstream>
#include <vector>
using namespace std;

ifstream is("ciur.in");
ofstream os("ciur.out");

int n, nr;
vector<int> x;

int main()
{
    is >> n;
    x = vector<int>(n+1, 1);
    x[1] = 0;
    for ( int i = 2; i * i <= n; i++ )
        if ( x[i] )
            for ( int j = 2; i * j <= n; j++ )
                x[i * j] = 0, nr++;
    os << n - nr;
    is.close();
    os.close();
    return 0;
}