diff --git a/changpu_v2.cc b/changpu_v2.cc
index 77893251adb1cbff4b78470ac858c7cf55660bef..28dbb7cb6e02cee795daed4525c0c0d17730c749 100644
--- a/changpu_v2.cc
+++ b/changpu_v2.cc
@@ -11,11 +11,11 @@ using namespace std::literals;
 
 // argument should be valid.
 inline char basic_int_to_char(uint8_t i) {
-    constexpr auto ls = "0A23456789JQK";
+    constexpr auto ls = "xA234567890JQK";
     return ls[i];
 }
 inline uint8_t basic_char_to_int(char c) {
-    constexpr auto ls {"0A23456789JQK"sv};
+    constexpr auto ls {"xA234567890JQK"sv};
     return ls.find(c);
 }
 
diff --git a/changpu_v2.py b/changpu_v2.py
index fe156bf194a3a6f374880c9dc536a9a9db392271..1fc2f07e2cddc886273e5d100af00b21a75150c6 100644
--- a/changpu_v2.py
+++ b/changpu_v2.py
@@ -9,10 +9,10 @@ else:
 import itertools
 
 def basic_char_to_int(ch):
-    ls = '0A23456789JQK'
+    ls = 'xA234567890JQK'
     return ls.find(ch)
 def basic_int_to_char(i):
-    ls = '0A23456789JQK'
+    ls = 'xA234567890JQK'
     return ls[i]
 
 def comb_exclude_border(ar):