#include <fstream>

using namespace std;

const int Nmax = 2000000;

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

int k = 1, i, j, n;
bool ciur[Nmax];

int main()
{
    fin >> n;
    if (n == 2)
    {
        fout<<"1\n";
        return 0;
    }
    for (i = 2; i <= n; ++i)
        ciur[i] = 1;
    for (i = 2; i * i <= n; ++i)
        if (ciur[i])
            for (j = i * i; j <= n; j += i)
                ciur[j] = 0;
    for (i = 3; i <= n; i += 2)
    {
        if (ciur[i])
            ++k;
    }
    fout << k << "\n";
    return 0;
}