Change the name of input files.

day1.cr

@@ -1,4 +1,4 @@
-changes = File.read("day1").split("\n")
+changes = File.read("day1_input").split("\n")
   .select { |it| !it.empty? } 
   .map(&.to_i)
 

day2.cr

@@ -1,6 +1,6 @@
 require "./common.cr"
 
-lines = File.read("day2").split("\n")
+lines = File.read("day2_input").split("\n")
 lines.pop
 
 CHARS = ('a'..'z').to_a

day3.cr

@@ -1,6 +1,6 @@
 require "./common.cr"
 
-lines = File.read("day3").split("\n")
+lines = File.read("day3_input").split("\n")
 lines.pop
 
 REGEX = /#([0-9]+) @ ([0-9]+),([0-9]+): ([0-9]+)x([0-9]+)/