#include <fstream>

using namespace std;

const int VMAX = 2e6;

ifstream cin("ciur.in");
ofstream cout("ciur.out");


bool v[VMAX+1];


int main()
{
    int n;
    cin>>n;

    int prime = n-1;

    for (int i = 2; i*i<=n; i++)
    {
        if (v[i]==0)
        {
            for (int j = i*i; j<=n; j+=i)
            {
                v[j]=1;
                prime--;
            }
        }
    }

    cout<<prime;
    return 0;
}