#include<fstream>
#include<cmath>
using namespace std;
int main()
{
    fstream in("ciur.in");
    fstream out("ciur.out");
    int N,i,j,suma=0,p;
   bool v[2000001]={0};
    in>>N;
    for(i=2;i<=N;i++)
        if(v[i]==0)
       {

         for(j=i+i;j<=N;j=j+i)

        v[j]=1;
        suma=suma+1;
    }
        out<<suma;
        in.close();
        out.close();
    return 0;
}