diff --git a/subjects/doop.en.md b/subjects/doop.en.md
index fd67dc190..3f362370b 100644
--- a/subjects/doop.en.md
+++ b/subjects/doop.en.md
@@ -10,10 +10,14 @@ The program has to be used with three arguments:
 - An operator
 - Another value
 
+The following operators are considered valid: "+", "-", "/", "*", "%".
+
 In case of an invalid operator the programs prints `0`.
 
 In case of an invalid number of arguments the program prints nothing.
 
+In case of overflow the program prints **Overflow**.
+
 The program has to handle the modulo and division operations by 0 as shown on the output examples below.
 
 `fmt.Print` is authorized.
@@ -33,6 +37,8 @@ student@ubuntu:~/piscine-go/test$ ./doop 1 / 0 | cat -e
 No division by 0$
 student@ubuntu:~/piscine-go/test$ ./doop 1 % 0 | cat -e
 No Modulo by 0$
+student@ubuntu:~/piscine-go/test$ ./doop 9223372036854775807 + 1
+Overflow
 student@ubuntu:~/piscine-go/test$ ./doop 1 "*" 1
 1
 student@ubuntu:~/piscine-go/test$ ./doop 1 "*" -1