Language: C++

import Control.Monad

main :: IO ()
main = do
    [n, k] <- map read . words <$> getLine :: IO [Integer]
    pos <- replicateM (fromIntegral n) ((\[a,b]->(a,b)) . map read . words <$> getLine) :: IO [(Integer, Integer)]
    ns <- concat <$> mapM (innerPoints pos k) [(p, p',p'')| p<-pos, p'<-pos, p''<-pos]
    print . minimum $ ns

innerPoints :: [(Integer, Integer)] 
            -> Integer
            -> ((Integer,Integer), (Integer,Integer), (Integer,Integer))
            -> IO [Integer]
innerPoints pos k ((x,y), (x', y'),(x'', y'')) = let
    isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
                         && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
    innerP = sum . map (\b->if b then 1 else 0) $ map isInner pos
    in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]



Compiler output:
a.cc:6:42: error: stray '\' in program
    6 |     pos <- replicateM (fromIntegral n) ((\[a,b]->(a,b)) . map read . words <$> getLine) :: IO [(Integer, Integer)]
      |                                          ^
a.cc:7:53: warning: multi-character character constant [-Wmultichar]
    7 |     ns <- concat <$> mapM (innerPoints pos k) [(p, p',p'')| p<-pos, p'<-pos, p''<-pos]
      |                                                     ^~~~
a.cc:7:57: warning: multi-character literal with 12 characters exceeds 'int' size of 4 bytes
    7 |     ns <- concat <$> mapM (innerPoints pos k) [(p, p',p'')| p<-pos, p'<-pos, p''<-pos]
      |                                                         ^~~~~~~~~~~~~~
a.cc:7:79: error: empty character constant
    7 |     ns <- concat <$> mapM (innerPoints pos k) [(p, p',p'')| p<-pos, p'<-pos, p''<-pos]
      |                                                                               ^~
a.cc:14:29: warning: multi-character character constant [-Wmultichar]
   14 | innerPoints pos k ((x,y), (x', y'),(x'', y'')) = let
      |                             ^~~~~
a.cc:14:38: error: empty character constant
   14 | innerPoints pos k ((x,y), (x', y'),(x'', y'')) = let
      |                                      ^~
a.cc:14:43: error: empty character constant
   14 | innerPoints pos k ((x,y), (x', y'),(x'', y'')) = let
      |                                           ^~
a.cc:15:15: error: empty character constant
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |               ^~
a.cc:15:17: warning: multi-character character constant [-Wmultichar]
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                 ^~~~~
a.cc:15:22: error: empty character constant
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                      ^~
a.cc:15:41: warning: multi-character character constant [-Wmultichar]
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                         ^~~~
a.cc:15:45: warning: multi-character literal with 6 characters exceeds 'int' size of 4 bytes
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                             ^~~~~~~~
a.cc:15:53: error: empty character constant
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                                     ^~
a.cc:15:60: error: empty character constant
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                                            ^~
a.cc:15:62: warning: multi-character literal with 16 characters exceeds 'int' size of 4 bytes
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                                              ^~~~~~~~~~~~~~~~~~
a.cc:15:82: error: empty character constant
   15 |     isInner (x''', y''') =  minimum [x,x',x''] <= x''' && x''' <= maximum [x,x',x'']
      |                                                                                  ^~
a.cc:16:41: warning: multi-character character constant [-Wmultichar]
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                         ^~~~
a.cc:16:45: warning: multi-character literal with 6 characters exceeds 'int' size of 4 bytes
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                             ^~~~~~~~
a.cc:16:53: error: empty character constant
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                                     ^~
a.cc:16:60: error: empty character constant
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                                            ^~
a.cc:16:62: warning: multi-character literal with 16 characters exceeds 'int' size of 4 bytes
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                                              ^~~~~~~~~~~~~~~~~~
a.cc:16:82: error: empty character constant
   16 |                          && minimum [y,y',y''] <= y''' && y''' <= maximum [y,y',y'']
      |                                                                                  ^~
a.cc:17:25: error: stray '\' in program
   17 |     innerP = sum . map (\b->if b then 1 else 0) $ map isInner pos
      |                         ^
a.cc:18:29: warning: multi-character character constant [-Wmultichar]
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                             ^~~~
a.cc:18:33: warning: multi-character literal with 14 characters exceeds 'int' size of 4 bytes
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                                 ^~~~~~~~~~~~~~~~
a.cc:18:51: error: empty character constant
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                                                   ^~
a.cc:18:71: warning: multi-character character constant [-Wmultichar]
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                                                                       ^~~~
a.cc:18:75: warning: multi-character literal with 16 characters exceeds 'int' size of 4 bytes
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                                                                           ^~~~~~~~~~~~~~~~~~
a.cc:18:95: error: empty character constant
   18 |     in return [(maximum [x,x',x'']-minimum [x,x',x'']) * (maximum [y,y',y''] - minimum [y,y',y'']) | innerP >= k]
      |                                                                                               ^~
a.cc:1:1: error: 'import' does not name a type
    1 | import Control.Monad
      | ^~~~~~
a.cc:1:1: note: C++20 'import' only available with '-fmodules-ts'