# coding: utf-8

# 入力１行目：4桁の整数(１文字列)
s = gets.chomp.split("")

# ソート
s.sort!

ans = "No"
if s[0] == s[1] and s[2] == s[3] and s[0] != s[2]
    if /[A-Z]/ === s[0] and /[A-Z]/ === s[2]
        ans = "Yes"
    end
end

puts ans
