#include <fstream>
#include <cmath>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int main()
{
    bool v[2000001]={0};
    long n;
    int i,j,gogu=0;
    in>>n;
    for(i=2;i<=sqrt(n);i++)
    if(v[i]==0)
        for(j=i+i;j<=n;j=j+i)
               v[j]=1;
    for(i=2;i<=n;i++)
        if(!v[i]) gogu++;
    out<<gogu;
    in.close();
    out.close();
    return 0;

}