#include <fstream>

using namespace std;

int prim (int a)
{
    int c = 1;
    if (a < 2)
        return 0;
    for (int i = 2; i*i <= a && c == 1; i++)
        if (a%i == 0)
            c--;
    return c;
}

int main()
{
    ifstream fi ("ciur.in");
    ofstream fo ("ciur.out");
    int N, c;
    c = 1;
    fi >> N;
    for (int i = 3, d = 1; i <= N; i+=2)
        if (prim(i) == 1)
            c++;
    fo << c;
    return 0;
}