#include <fstream>
using namespace std;

int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int n, nr = 1;
    fin >> n;
    int prim[n];

    for(int i = 1; ((i * i) << 1) + (i << 1) <= n; i += 1)
    {
        if(prim[i] == 0){
            for(int j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i << 1) + 1)
                prim[j] = 1;
        }
    }

    for (int i=1; 2 * i + 1 <= n; ++i)
        if (prim[i] == 0) nr++;

    fout << nr;

    return 0;
}