#!/usr/bin/ruby
# encoding: utf-8

s = gets.chomp

if (s[0] == s[1] and s[2] == s[3] and s[1] != s[2]) or (s[0] == s[3] and s[1] == s[2] and s[0] != s[1]) or (s[0] == s[2] and s[1] == s[3] and s[0] != s[1])
  puts "Yes"
else
  puts "No"
end