one.js

// Find Answer
function solve(arr) {
  const map = {};

  for (let i = 0; i < arr.length; i++) {
    if (map[Number(arr[i])]) {
      return Number(arr[i]) * (2020 - Number(arr[i]));
    } else {
      map[2020 - Number(arr[i])] = true;
    }
  }

  return "Happy Christmas";
}

// Helper Function
function convert(str) {
  return str.split("\n");
}

// Inputs
let input = convert(`1535
1908
1783
1163
1472
1809
1566
1919
1562
1532
1728
1999
1942
337
1135
2006
1083
1483
1688
1511
1134
1558
1139
1790
1406
1255
1627
1941
1619
2009
1453
1806
1756
1634
1026
1847
1520
1914
1836
1440
1839
1527
1638
1642
1776
1148
1958
1616
1952
1092
1081
1898
1487
2000
1921
1579
54
1031
1842
1006
1781
1964
168
1339
1094
1997
1522
1962
1837
1730
1244
1593
1752
1400
1330
1649
1639
1493
1696
2003
1612
1717
1835
861
1950
1896
557
1926
571
1725
1229
1213
1625
1553
1204
1459
1666
1723
1118
1845
1663
1829
1929
1880
1738
1887
1605
1273
1759
1932
1156
1712
1767
1241
1159
1476
1705
1768
1680
1543
2010
1849
1289
1636
1894
1823
1706
1239
1802
1744
1584
1690
1758
1618
1749
1521
1594
1960
1479
1022
1559
1106
1755
1254
1878
1243
1418
1671
1895
1120
1673
1719
1904
724
1945
1940
1819
1939
1103
2008
1791
1874
1544
1892
1557
1617
1998
1641
1907
1563
1089
1086
1276
1591
1614
1216
1658
1514
1899
1760
1797
1831
277
1622
1795
1468
1537
1742
1709
1886
1846
1567
1492
1549
1587
1818
1687
1404
1778
1096`);

// result
console.log(solve(input));