fix string error

app.py

@@ -15,7 +15,7 @@ uploaded_file = st.file_uploader("Upload JSON File", type=["json"])
 if uploaded_file:
     loaded_dict = json.load(uploaded_file)
     df = pd.DataFrame(loaded_dict)
-    st.subheader(len(df)+" sentiment tuples was detected")
+    st.subheader(f"{len(df)}+ sentiment tuples was detected")
     st.write(df)
 
     # Sentiment Distribution Chart