Merkkijono

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class B {

	public static void main(String[] args) {
		FastReader reader = new FastReader();
		PrintWriter writer = new PrintWriter(new OutputStreamWriter(System.out));

		int n = reader.nextInt();
		reader.close();

		writer.println(solve(n));

		writer.flush();
		writer.close();
	}

	public static String solve(int n) {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < n; i++) {
			char a = (char) (97 + i); // Go through every character from a to p
			for (int j = sb.length(); j >= 0; j -= 1) { // Go through every index of string and insert letter there
				sb.insert(j, a);
			}
		}
		return sb.toString();
	}

	static class FastReader {

		BufferedReader br;
		StringTokenizer st;

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			br = null;
			st = null;
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}

			}
			return st.nextToken();
		}

		String nextLine() {
			String str = "";
			if (st.hasMoreElements()) {
				str = st.nextToken("\n");
			} else {
				try {
					str = br.readLine();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return str;
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

	}

}

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