#include <fstream>

using namespace std;

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


///Ciurul lui Eratosthenes

bool v[2000001];

int main()
{
    int x, i=3, j, nr=1;
    fin >> x;

    for (i; i<=x; i+=2)
    {
        if (v[i] == 0)
        {
            nr++;
            for (j=i+i+i; j<=x; j+=i+i+i)
                v[j]=1;
        }
    }
    fout << nr;

    return 0;
}