'use strict';

function ary_counter(ary) {
  let c = 0;
  ary.forEach(a => ++c);
  return c;
}

function main(stdin) {
  const l = [];
  let res = 'Yes';

  for (let i = 0; i < 4; ++i) {    
    const c = stdin.charCodeAt(i);
    l[c] = l[c] || 0;
    ++l[c];
  }

  if (ary_counter(l) !== 2) res = 'No'; 
  
  console.log(res);
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));