diff --git a/LeetcodeProblems/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js b/LeetcodeProblems/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js
index b589871..c438988 100644
--- a/LeetcodeProblems/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js
+++ b/LeetcodeProblems/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js
@@ -61,11 +61,8 @@ var TreeNode = function(val) {
   this.left = this.right = null;
 }
 
-console.log(
-  buildTree(
-    [3,9,20,15,7],
-    [9,3,15,20,7]
-  )
-);
+var main = function() {
+  console.log(buildTree([3,9,20,15,7], [9,3,15,20,7]));
+}
 
 module.exports.main = main
diff --git a/Main.js b/Main.js
index 1967baf..9689d6f 100644
--- a/Main.js
+++ b/Main.js
@@ -9,8 +9,12 @@ var main = async function() {
     for(i in problems) { 
       console.log("Solving: " + problems[i] + ":");
       const problem = require(PROBLEMS_FOLDER + problems[i]);
-      problem.main();
-      console.log("End of the solution for : " + problems[i] + ",\n\n");
+      if (typeof(problem.main) !=='undefined') {
+        problem.main();
+        console.log("End of the solution for : " + problems[i] + ",\n\n");
+      } else {
+        console.warn(problem, "The problem " + problems[i] +  " doesn't have a main method implemented.");
+      }
     }
   } catch (error) {
     throw new Error(error);
@@ -23,8 +27,8 @@ var loadProblems = () => {
       if (error) {
         reject(error);
       } else {
-	problems = files.filter(item => !(REGEX_PATTERN_HIDDEN_FILES).test(item));
-	resolve(problems);
+        problems = files.filter(item => !(REGEX_PATTERN_HIDDEN_FILES).test(item));
+        resolve(problems);
       }
     })
   });