text: 'use strict';
  
  const add = (n, acc = 0) => {
      if (n === 0) return acc;
      return add(n - 1, acc + n);
  };
  
  console.log(add(3));
  
  const tail = (n, acc = 0) => {
      while (true) {
          if (n === 0) return acc;
          acc += n;
          n--;
      }
  };
  
  console.log(tail(3));