#include <fstream>

using namespace std;

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

char V[2100000];



int main()
{
    int i, j, n, k=0;
    in >> n;

    for (i = 2; i <= n; i++)
    {
        if (V[i] == 1)
            continue;
        k++;
        for (j = i * i; j <= n; j = j + i)
            V[j] = 1;

    }
    out << k;
    return 0;
}