#include <fstream>
#include <cmath>
#include <algorithm>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000005];
int main()
{
   int n,i,j,nr=0;
   in>>n;
   for(j=2;j*2<=n;j++)
      v[j*2]=1;
   for(i=3;i*i<=n;i=i+2)
   {
       if(v[i]==0)
       for(j=2;j*i<=n;j++)
          v[i*j]=1;
   }
   for(i=2;i<=n;i++)
     if(v[i]==0)
       nr++;
   out<<nr;
}