#include <fstream>
#define N 2000001
using namespace std;
ifstream in ("ciur.in");
ofstream out("ciur.out");
bool prim[N];
int main()
{
    int n,p=2,nr=0;
    in>>n;
    while (p*p<=n){
    for (int i=2;i<=n/p;i++)
    {
        prim[i*p]=1;
        p++;
        while (prim[p]==1)p++;
    }
    }
    for (int i=2;i<=n;i++)
        if (prim[i]==0) nr++;
    out<<nr;
    return 0;
}