Please place markers as following
              ``..................``              
           `..........................`           
         `..............................`         
       ....................................       
     ........................................     
    ........X........................X........    
  `............................................`  
 `.........  `......................`  .........` 
 .........    ......................    ......... 
 .........    `.........X..........`    ......... 
..........    ......................    ..........
...........```......................```...........
..................................................
..................................................
 ........X.............X.................X....... 
 ..........                            .......... 
 `..........                          ..........` 
  `...........`                    `...........`  
    ............`                `............    
     ..............`          `..............     
       ..................X.................       
         `..............................`         
            ..........................            
              ```................```        