#include <iostream>
#include <fstream>

using namespace std;

int N, nr_prime;
bool prim[2000005];

int main()
{
    int i, j;

    ifstream in("ciur.in");
    in>> N;
    in.close();

    for (i = 2; i <= N; ++i)
    {
        prim[i] = 1;
    }

    for (i = 2; i <= N; ++i)
    {
        if (prim[i])
        {
            nr_prime++;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
    }
    ofstream out("ciur.out");
    out<< nr_prime;
    out.close();

    return 0;
}