diff --git a/RepoSize/model.py b/RepoSize/model.py
index 15ff8b1..3bd93ce 100644
--- a/RepoSize/model.py
+++ b/RepoSize/model.py
@@ -1,10 +1,24 @@
 import argparse
+import re
+import sys
 
 parser =argparse.ArgumentParser(prog="reposize",description="Find the size of the specifed Github repository. Used this way: python reposize lucidrains/toolformer-pytorch",epilog="Thanks for using %(prog)s!")
 
-parser.add_argument("<user/repo>")
-parser.add_argument("-v","--version",action="version",version="%(prog)s 1.0.0")
+parser.add_argument("repository")
+parser.add_argument("-v","--version",action="version",version="%(prog)s 1.1.0")
 
 arguments = parser.parse_args()
 target_repo = arguments.repository
 
+pattern = "^[a-zA-Z0-9_.-]+\/[a-zA-Z0-9_.-]+$"
+
+match = re.match(pattern, target_repo)
+try:
+    if not match:
+        raise ValueError("Invalid input")
+except ValueError as e:
+    print(e)
+    print("Please enter a valid Github repository in the form <user>/<repository>")
+    sys.exit(1)
+
+
diff --git a/RepoSize/reposize.py b/RepoSize/reposize.py
index 4e8d893..cc8f0e2 100644
--- a/RepoSize/reposize.py
+++ b/RepoSize/reposize.py
@@ -2,7 +2,7 @@
 import model
 
 def requester(request):
-
+    
     response = requests.get(
         "https://api.github.com/repos/"+str(request)
     )