#include <fstream>

using namespace std;

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

int v[2000001];

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