add feature flag

src/lib.rs

@@ -1,5 +1,6 @@
 #![feature(let_chains)]
 #![feature(decl_macro)]
+#![feature(iter_array_chunks)]
 
 pub mod days;
 pub mod utils;

src/prelude.rs

@@ -5,3 +5,5 @@ pub use std::{
     collections::{ HashMap as M, HashSet as S },
     cmp::Ordering as Or,
 };
+
+pub type SS = &'static str;