import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.InputMismatchException;
import java.util.Map.Entry;
import java.util.NoSuchElementException;

public class Main implements Runnable { // クラス名はMain1

	PrintWriter out = new PrintWriter(System.out);
	InputReader sc = new InputReader(System.in);

	public static void main(String[] args) {
		Thread.setDefaultUncaughtExceptionHandler((t, e) -> System.exit(1));
		new Thread(null, new Main(), "", 1024 * 1024 * 1024).start(); // 16MBスタックを確保して実行
	}

	public void run() {

		try {
			//String S = sc.next().trim();
			int N = sc.nextInt();
			int[] D = new int[N];
			boolean[] time = new boolean[24];
			HashMap<Integer, Integer> hm = new HashMap<>();
			for (int i = 0; i < N; i++) {
				int d = sc.nextInt();
				D[i] = d;
				if (hm.containsKey(d)) {
					int count = hm.get(d) + 1;
					hm.put(d, count);
				} else {
					hm.put(d, 1);
				}
			}

			ArrayList<Integer> one = new ArrayList<Integer>();

			time[0] = true;
			for (Entry<Integer, Integer> e : hm.entrySet()) {
				if (e.getKey() == 0) {
					out.println(0);
					return;
				} else if (e.getKey() == 0 || e.getKey() == 12) {
					time[e.getKey()] = true;
					if (e.getValue() >= 2) {
						out.println(0);
						return;
					}
				} else {
					if (e.getValue() >= 3) {
						out.println(0);
						return;
					} else if (e.getValue() >= 2) {
						time[e.getKey()] = true;
						time[24 - e.getKey()] = true;
					} else {
						one.add(e.getKey());
					}
				}
			}

			int ans = 0;
			for (int bit = 0; bit < (1 << one.size()); bit++) {
				//out.println("bit:" + Integer.toBinaryString(bit));
				boolean[] times = time.clone();
				for (int j = 0; j < one.size(); j++) {
					if ((1 & bit >> j) == 1) {
						//out.println(j + " " + one.get(j));
						times[one.get(j)] = true;
					} else {
						times[24 - one.get(j)] = true;
					}
				}
				//out.println("time :" + Arrays.toString(time));
				//out.println("times:" + Arrays.toString(times));

				int min = Integer.MAX_VALUE;
				out: for (int i = 0; i < 23; i++) {
					if (times[i]) {
						for (int j = i + 1; j < 24; j++) {
							if (times[j]) {
								int w = Math.min(j - i, 24 - j + i);
								min = Math.min(min, w);
							}
						}
					}
				}
				ans = Math.max(ans, min);

			}

			out.println(ans);

		} catch (ArithmeticException ae) {
			//ae.printStackTrace();
			throw new RuntimeException();
		} catch (Exception e) {
			e.printStackTrace();
			throw new RuntimeException();
		} finally {
			out.flush();
			out.close();
		}

	}

	///////////////////////////////////////////////////////////
	//Ignore
	///////////////////////////////////////////////////////////
	static class InputReader {
		private InputStream in;
		private byte[] buffer = new byte[1024];
		private int curbuf;
		private int lenbuf;

		public InputReader(InputStream in) {
			this.in = in;
			this.curbuf = this.lenbuf = 0;
		}

		public boolean hasNextByte() {
			if (curbuf >= lenbuf) {
				curbuf = 0;
				try {
					lenbuf = in.read(buffer);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (lenbuf <= 0)
					return false;
			}
			return true;
		}

		private int readByte() {
			if (hasNextByte())
				return buffer[curbuf++];
			else
				return -1;
		}

		private boolean isSpaceChar(int c) {
			return !(c >= 33 && c <= 126);
		}

		private void skip() {
			while (hasNextByte() && isSpaceChar(buffer[curbuf]))
				curbuf++;
		}

		public boolean hasNext() {
			skip();
			return hasNextByte();
		}

		public String next() {
			if (!hasNext())
				throw new NoSuchElementException();
			StringBuilder sb = new StringBuilder();
			int b = readByte();
			while (!isSpaceChar(b)) {
				sb.appendCodePoint(b);
				b = readByte();
			}
			return sb.toString();
		}

		public int nextInt() {
			if (!hasNext())
				throw new NoSuchElementException();
			int c = readByte();
			while (isSpaceChar(c))
				c = readByte();
			boolean minus = false;
			if (c == '-') {
				minus = true;
				c = readByte();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res = res * 10 + c - '0';
				c = readByte();
			} while (!isSpaceChar(c));
			return (minus) ? -res : res;
		}

		public long nextLong() {
			if (!hasNext())
				throw new NoSuchElementException();
			int c = readByte();
			while (isSpaceChar(c))
				c = readByte();
			boolean minus = false;
			if (c == '-') {
				minus = true;
				c = readByte();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res = res * 10 + c - '0';
				c = readByte();
			} while (!isSpaceChar(c));
			return (minus) ? -res : res;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

		public int[] nextIntArray(int n) {
			int[] a = new int[n];
			for (int i = 0; i < n; i++)
				a[i] = nextInt();
			return a;
		}

		public long[] nextLongArray(int n) {
			long[] a = new long[n];
			for (int i = 0; i < n; i++)
				a[i] = nextLong();
			return a;
		}

		public char[][] nextCharMap(int n, int m) {
			char[][] map = new char[n][m];
			for (int i = 0; i < n; i++)
				map[i] = next().toCharArray();
			return map;
		}
	}
}


Measured memory_bytes: 35544