From 3605f3204fc378a3b55e417b79c7d68d25c649e4 Mon Sep 17 00:00:00 2001
From: nwerc-082 <nwerc-082@nwerc-082.bath.ac.uk>
Date: Sat, 19 Nov 2016 10:42:12 +0000
Subject: [PATCH] ...

---
 C.py | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 C.py

diff --git a/C.py b/C.py
new file mode 100644
index 0000000..fea3a6b
--- /dev/null
+++ b/C.py
@@ -0,0 +1,5 @@
+from __future__ import print_function
+import sys
+P = sys.stdin.readline().rstrip()
+N = 26-len(set(P))
+print(N if N != 0 else "impossible")