#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");

int main()
{
    int n, i, j, c=0, nc;
    bool ciur[2000000];
    in>>n;
nc=n;
    for (i=4; i<=2000000; i+=2)
    {
        ciur[i]=1;
    }
    for (i=3; i<=2000000; i+=2)
    {
        for (j=2; i*j<=2000000; j++)
        {
            ciur[i*j]=1;
        }
    }
    //out<<nc;
    ciur[1]=1;
    for (i=1; i<=nc; i++)
    {
        if (ciur[i]==0) c++;
        // out<<i<<" ";


    }
     out<<c;

    return 0;
}