let dec = process.argv[2];
let result = '';

const getChar = char =>
  ({
    '10': 'A',
    '11': 'B',
    '12': 'C',
    '13': 'D',
    '14': 'E',
    '15': 'F'
  }[char] || char);

do {
  const float = dec / 16;
  const int = (dec = Math.floor(float));
  const remainder = (float - int) * 16;

  result = getChar(remainder) + result;
} while (dec !== 0);

console.log(result);