diff --git a/src/cipher_analytical_machine/parsers/parsers.clj b/src/cipher_analytical_machine/parsers/parsers.clj
index e0ef1dd..e932f2e 100644
--- a/src/cipher_analytical_machine/parsers/parsers.clj
+++ b/src/cipher_analytical_machine/parsers/parsers.clj
@@ -3,7 +3,21 @@
   (:gen-class))
 
 (defn unsigned-int?
+  "Return true if the string is an unsigned integer."
   [str]
   (if (re-matches #"\d+" str)
     true false))
 
+(defn parse-unsigned-int
+  "Return an integer if the argument is an integer."
+  [str-or-int]
+  (cond
+    (int? str-or-int)
+    str-or-int
+
+    (unsigned-int? str-or-int)
+    (Integer/parseInt str-or-int)
+
+    :else
+    nil))
+
diff --git a/test/cipher_analytical_machine/parsers/parsers_test.clj b/test/cipher_analytical_machine/parsers/parsers_test.clj
index ab723ef..75556e0 100644
--- a/test/cipher_analytical_machine/parsers/parsers_test.clj
+++ b/test/cipher_analytical_machine/parsers/parsers_test.clj
@@ -4,7 +4,7 @@
    [cipher-analytical-machine.parsers.parsers :refer :all]))
 
 (deftest unsigned-int?-test
-  (testing ""
+  (testing "The function return true only for an unsingned integer as a string."
     (are [str expected]
         (= expected
            (unsigned-int? str))
@@ -13,3 +13,13 @@
       "-10" false
       "abc" false)))
 
+(deftest parse-unsigned-int-test
+  (testing "The function parse the integer if the string is an integer."
+    (are [str-or-int expected]
+        (= expected
+           (parse-unsigned-int str-or-int))
+      "9"   9
+      9     9
+      "10"  10
+      "-10" nil
+      "abc" nil)))