#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n,stop,numPrime = 1;

bool prime[2000000 / 2 + 2];

int main()
{
    f >> n;

    int stop = (n - 1) / 2;

    for(int k = 1; k <= stop; k++)
        if(!prime[k])
        {
            ++numPrime;
            for(int i = 3 * k + 1; i <= stop; i += 2 * k + 1)
                prime[i] = true;
        }

    g << numPrime;

    return 0;
}