20250419 finished.

src/problem/mod.rs

@@ -607,3 +607,5 @@ mod p2537_count_the_number_of_good_subarrays;
 mod p2176_count_equal_and_divisible_pairs_in_an_array;
 
 mod p2364_count_number_of_bad_pairs;
+
+mod p2563_count_the_number_of_fair_pairs;