Calculate also KEY_FONT_SIZE

diff --git a/qwerty.py b/qwerty.py
index 1deb0fa..1c92641 100755
--- a/qwerty.py
+++ b/qwerty.py
@@ -33,7 +33,7 @@ LABEL_FONT_SIZE_COEF = 0.016
 DESC_TOP = 110
 DESC_FONT_SIZE_COEF = 0.014
 KEY_BOTTOM = 35
-KEY_FONT_SIZE = 40
+KEY_FONT_SIZE_COEF = 0.039

 LINEHEIGHT = 1.2

@@ -560,6 +560,7 @@ class GUI(object):
         global sections
         global LABEL_FONT_SIZE
         global DESC_FONT_SIZE
+        global KEY_FONT_SIZE

         self.buttons = {}
         self.sbuttons = []
@@ -582,6 +583,7 @@ class GUI(object):

         LABEL_FONT_SIZE = LABEL_FONT_SIZE_COEF * self.height
         DESC_FONT_SIZE  = DESC_FONT_SIZE_COEF  * self.height
+        KEY_FONT_SIZE   = KEY_FONT_SIZE_COEF   * self.height

         for c in ALPHABET:
             self.buttons[c] = SuperButton(c)