#include <fstream>
#include <iostream>

using namespace std;

bool prim[2000001];
unsigned int n, d, m, prime,i;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    fin >> n;
    for (d = 2; d <= n; d++)
        prim[d] = true;
    for (d = 2; d <= n; d++)
        if (prim[d]) {
            prime++;
            for (m = 2 * d; m <= n; m += d)
                prim[m] = false;
        }
    fout << prime;
    return 0;
}
/*
2 3 4 5 6 7 8 9 0 1 2
t   .   .   .   .   .
  t     .     .     .
                .
*/