function freq(acc, next){
   if(acc[next] === undefined)
       acc[next] = 1;
   else
       acc[next] += 1;

   return acc
}


/*
  take two sets and returns a elements than differ in frequency.
*/
function processData(a,b) {
    //Enter your code here
    var sets = input.split('\n');

    var setOne = a.split(' ').reduce(freq, {});
    var setTwo = b.split(' ').reduce(freq, {});

    var lostSet = Object.keys(setOne).filter((key)=>setOne[key] !== setTwo[key]).sort();

    console.log(lostSet.join(' '))
}