diff --git a/apps/katapotter/src/app/game.spec.ts b/apps/katapotter/src/app/game.spec.ts
index 96e543f..f28f554 100644
--- a/apps/katapotter/src/app/game.spec.ts
+++ b/apps/katapotter/src/app/game.spec.ts
@@ -1,16 +1,23 @@
 import { Game } from './game';
 
 describe('Game', () => {
+  let game : Game;
+  beforeEach(() => {
+    game = new Game();
+  });
+
+  it('should create an instance', () => {
+    expect(game).toBeTruthy();
+  });
 
   test('buy one', () => {
-    const game = new Game();
-    game.buy(1);
+    game.buy("p1", 1);
     expect(game.price).toBe(100);
   });
 
   test('buy two', () => {
-    const game = new Game();
-    game.buy(2);
+    game.buy("p1", 1);
+    game.buy("p2", 1);
     expect(game.price).toBe(190);
   });
 });
diff --git a/apps/katapotter/src/app/game.ts b/apps/katapotter/src/app/game.ts
index f0fe02b..ac5d108 100644
--- a/apps/katapotter/src/app/game.ts
+++ b/apps/katapotter/src/app/game.ts
@@ -1,6 +1,44 @@
 export class Game {
-    buy(pins: number){}
+    // private _price = 0;
+    private booksvector: bookinfo[] = [];
+    private discount: number[] = [1, 0.95, 0.9, 0.8, 0.75];
+
+    buy(bookname: string, num: number){
+        let flag = false;
+        for( let i=0;i<this.booksvector.length;i++ ){
+            if(this.booksvector[i].name == bookname){
+                flag = true;
+            }
+        }
+        if(flag == false){
+            // let book = foo(bookname, num);
+            this.booksvector.push(foo(bookname, num))
+        }
+    }
     get price(){
-        return 100;
+        let final_price = 0;
+        // console.log(this.booksvector.length)
+        for( let i=0;i<this.booksvector.length;i++ ){
+            final_price += this.booksvector[i].len * 100;
+            // console.log(this.booksvector[i].len)
+            // console.log(this.booksvector[i].name)
+        }
+
+        final_price = final_price * this.discount[this.booksvector.length-1];
+
+        return final_price;
     }
-}
\ No newline at end of file
+}
+
+interface bookinfo{
+    name: string;
+    len: number;
+}
+
+function foo(name_: string, len_: number): bookinfo { 
+    return {
+        name: name_,
+        len: len_
+    };
+}
+