#!/usr/bin/awk -f
# HP20090909
# cat xxx | sort | printdup dup=3
BEGIN {
  old = "";
  dup = 1;
  cnt = 0;
}
  
{
  if ($0 != old) {
    cnt = 1;
  }
  else {
    cnt++;
  }
  if (cnt == dup) {
    print $0;
  }  
  old = $0;
}