import std.stdio;
import std.algorithm;
import std.math;
import std.conv;
import std.string;

T readNum(T)(){
  return readStr.to!T;
}

T[] readNums(T)(){
  return readStr.split.to!(T[]);
}

string readStr(){
  return readln.chomp;
}

void main(){
  auto s = readStr;
  int[char] dic;

  foreach(c; s){
    dic[c]++;
  }

  foreach(i; dic.byValue){
    if(i != 2){
      writeln("No");
      return;
    }
  }
  writeln("Yes");
}
