Update app.py

app.py

@@ -8,7 +8,7 @@ from langchain_community.tools import DuckDuckGoSearchRun
 from langchain.tools import Tool
 from langgraph.graph import START, StateGraph
 from langgraph.prebuilt import ToolNode, tools_condition
-from langchain_core.messages import AnyMessage, HumanMessage, AIMessage
+from langchain_core.messages import AnyMessage, HumanMessage, AIMessage, SystemMessage
 from typing import TypedDict, Annotated
 from langgraph.graph.message import add_messages