//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop

//---------------------------------------------------------------------------

#pragma argsused
#include <iostream.h>
  int r[13],p[100010];
  short a[13];

int main(int argc, char* argv[])
{
  int k,i,t,s,n;

  r[0]=1;k=2;s=0;
  while (1)
  {
    r[++s]=r[s-1]+k;
    if (r[s]>488889) break;
    k*=4;
  }

  for (i=1;i<10;i++)
    p[i]=i;
  for (i=10;i<100;i++)
    p[i]=i*2-9;
  for (i=100;i<1000;i++)
    p[i]=i*3-9-99;
  for (i=1000;i<10000;i++)
    p[i]=i*4-9-99-999;
  for (i=10000;i<100000;i++)
    p[i]=i*5-9-99-999-9999;

  a[0]=1;
  a[1]=3;
  a[2]=0;
  a[3]=6;
  a[4]=0;
  a[5]=6;
  a[6]=9;
  a[7]=0;
  a[8]=0;
  a[9]=7;

  while (cin>>n)
  {
    n=p[n];
    for (i=0;i<s;i++)
      if (n>=r[i] && n<r[i+1])
        break;
    cout<<a[i]<<endl;
  }

  return 0;
}
//---------------------------------------------------------------------------