Merkkijono

const input = () => new Promise(r => process.stdin.once("data", d => r(d.toString().trim())));
(async () => {
    // -- START --

    function add(str, chr) {
        return chr + str.split("").map(c => c + chr).join("");
    };

    const n = parseInt(await input());
    let ans = "";
    for (let i = 0; i < n; i++) {
      ans = add(ans, String.fromCharCode(97 + i));
    }
    console.log(ans);

    // -- END --
    process.exit(0);
})();

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED