diff --git a/Part1-Timing/graph.py b/Part1-Timing/graph.py
index 9eb1b01..aa1579b 100644
--- a/Part1-Timing/graph.py
+++ b/Part1-Timing/graph.py
@@ -1,10 +1,15 @@
 import os
 import json
+import sys
 import matplotlib.pyplot as plt
 import numpy as np
 from tqdm import tqdm
 from datetime import datetime
 
+if sys.version_info < (3,0):
+    print("Run me with python3, not python2!")
+    sys.exit(1)
+
 num_runs = 100
 dict_of_dict_of_lists = dict()
 
diff --git a/Part1-Timing/reference b/Part1-Timing/reference
index 7cad2c7..47337ac 100755
Binary files a/Part1-Timing/reference and b/Part1-Timing/reference differ