#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
 int n,sol=1; bool v[2000005];
 void Ciur()
 { int i,j;
    for(i=3;i*i<=n;i+=2)
     if (!v[i])
      {
         for(j=i*i;j<=n;j+=2*i)
          v[j]=1;
      }

    for(i=3;i<=n;i+=2)
      if (!v[i]) sol++;

   g<<sol;
 }
int main()
{ f>>n;
  Ciur();
    return 0;
}