#include <fstream>

using namespace std;

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

bool v[2000000];

int main()
{
    int n,k=0,j,i;
    in>>n;
    for (i=2; i<=n; i++)
    {
        if (v[i]==0)
        {
            for (j=i; j<=n; j=j+i)
            {
                v[j]=1;
            }
            k++;
        }
    }
    out<<k;
    return 0;
}