diff --git a/quad10/fenomens/lab/p4/str.f90 b/quad10/fenomens/lab/p4/str.f90
new file mode 100644
index 0000000..31cd529
--- /dev/null
+++ b/quad10/fenomens/lab/p4/str.f90
@@ -0,0 +1,6 @@
+character(len=20) function str(k)
+  ! "Convert an integer to string."
+  integer, intent(in) :: k
+  write (str, *) k
+  str = adjustl(str)
+end function str