#include<iostream>
#include<fstream>
using namespace std;
char v[2000005];
int main()
{ ifstream fin("ciur.in");
  ofstream fout("ciur.out");

    long long i,n,nr,j;
    fin>>n;
    nr=1;
    for(i=3;i<=n;i=i+2)
                { if(v[i]==0) {nr++;
                               for(j=i*i;j<=n;j=j+i)
                                  v[j]=1;}
                }
    fout<<nr;
    fout.close();
    fin.close();
    return 0;


}