function cappy(input = []) {
  const bottles = new Map();

  input.reduce((acc, curr) => {
    let [juice, quantity] = curr.split(" => ");
    quantity = Number(quantity);

    if(!acc.hasOwnProperty(juice)) {
        acc[juice] = 0;
    }
    acc[juice] += quantity;

    if (acc[juice] > 1000) {
      if (!bottles.has(juice)) {
        bottles.set(juice, 0);
      }

    bottles.set(juice, bottles.get(juice) + parseInt(acc[juice] / 1000));
      acc[juice] %= 1000;
    }

    return acc;
  }, {});


  for(let[juice, quantity] of bottles) {
      console.log(`${juice} => ${quantity}`);
  }
}