#include <fstream>

using namespace std;

ifstream ci ("ciur.in");
ofstream co ("ciur.out");

bool v[4000000];

int main()
{
    int n, r=1;
    ci >> n;
    for (int i=3; i<=n; i+=2)
    {
        if (v[i]==false)
        {
            r++;
            for (int j=i*i; j<=n; j+=i)
            {
                v[j]=true;
            }
        }
    }
    co << r;
    return 0;
}