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function perimeter(num) {
  let a = 1,
    b = 0,
    temp,
    arr = [];
  while (num >= 0) {
    temp = a;
    a = a + b;
    b = temp;
    arr.push(b);
    num--;
  }
  return arr.map(e => e * 4).reduce((a, b) => a + b);
}
console.log(perimeter(5)); // should be 80
console.log(perimeter(7)); // should be 216
console.log(perimeter(20)); // should be 114624
console.log(perimeter(30)); // should be 14098308