#include <fstream>

int main()
{
    std::ifstream mama("ciur.in");
    std::ofstream tata("ciur.out");
    int  n;
    bool c[2000001];
    int  counter;
    int  temp;

    mama >> n;
    
    for (int i = 2; i <= n; ++i)
    {
        c[i] = true;
    }
    
    counter = 0;
    for (int i = 2; i <= n; ++i)
    {
        if (c[i])
        {
            ++counter;
            temp = i;
            for (int j = 2 * i; j <= n; j += temp)
            {
                c[j] = false;
            }
        }
    }

    tata << counter;
    return 0;
}