#include <fstream>

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

int n;
bool prime[2000001];

int main()
{
    fin >> n;
    int contor = 0;

    prime[0] = prime[1] = true;
    for(int i = 2; i * i <= n; ++i)
        if(!prime[i])
    {

        for(int j = 2; j * i <= n; ++j)
        {

            prime[i * j] = true;
        }
    }
    for(int i = 1; i <= n; ++i)
        if(!prime[i])
            contor++;
    fout << contor;
    return 0;
}