Update app.py

app.py

@@ -608,7 +608,7 @@ Please provide:
 Format your response with clear headers and bullet points."""
 
         # Call OpenAI API
-        response = openai.ChatCompletion.create(
+        response = openai.chat.completions.create(
             model="gpt-4o",  # Using GPT-4 Omega model
             messages=[
                 {"role": "system", "content": "You are an expert mathematics professor grading student solutions."},