Update app.py

app.py

@@ -339,7 +339,7 @@ def generate_math_solution_openrouter(api_key, problem_text, history=None):
         
         # Create the completion
         completion = client.chat.completions.create(
-            model="microsoft/phi-4-reasoning-plus:free",
+            model="deepseek/deepseek-r1-0528:free",
             messages=messages,
             extra_headers={
                 "HTTP-Referer": "https://advancedmathtutor.edu",