#include <fstream>
using namespace std;

int n, answer;
bool prim[2000005];

int main()
{
    ifstream("ciur.in") >> n;
    for (int i = 2; i <= n; ++i)
        if (!prim[i])
        {
            ++answer;
            for (int j = i * i; j <= n; j += i)
                prim[j] = true;
        }
    ofstream("ciur.out") << answer;
}