#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)/2, 1);
    for ( int i = 2; i <= n; i++ )
        if ( x[i] )
        {
            nr++;
            for ( int j = i + i; j <= n; j += i )
                x[j] = 0;
        }
    os << nr;
    is.close();
    os.close();
    return 0;
}