diff --git a/cv7/a_station.c b/cv7/a_station.c
index c371e7e..bbb7c51 100644
--- a/cv7/a_station.c
+++ b/cv7/a_station.c
@@ -25,15 +25,15 @@ void destroy_station(struct station* station){
 }
 
 int select_track(struct station* station, const char* target){
-        if (target[0] >= 'A' && target[0] <= 'Z') {
-        return target[0] - 'A';
-
-        } else if (target[0] >= 'a' && target[0] <= 'z') {
-        return target[0] - 'a';
-
+       if (isalpha(target[0])) {
+        if (isupper(target[0])) {
+            return target[0] - 'A';
         } else {
-        return 0;
+            return target[0] - 'a';
         }
+    } else {
+        return 0;
+    }
 }
 
 void add_target_capacity(struct station* station,const char* target, int capacity){