Paul hates palindromes. He assumes that string s is tolerable if each its character is one of the first p letters of the English alphabet and s doesn't contain any palindrome contiguous substring of length 2 or more.

Paul has found a tolerable string s of length n. Help him find the lexicographically next tolerable string of the same length or else state that such string does not exist.

Input

The first line contains two space-separated integers: n and p (1 ≤ n ≤ 1000; 1 ≤ p ≤ 26). The second line contains string s, consisting of n small English letters. It is guaranteed that the string is tolerable (according to the above definition).

Output

If the lexicographically next tolerable string of the same length exists, print it. Otherwise, print "NO" (without the quotes).

Examples

Input

3 3
cba


Output

NO


Input

3 4
cba


Output

cbd


Input

4 4
abcd


Output

abda

Note

String s is lexicographically larger (or simply larger) than string t with the same length, if there is number i, such that s1 = t1, ..., si = ti, si + 1 > ti + 1.

The lexicographically next tolerable string is the lexicographically minimum tolerable string which is larger than the given one.

A palindrome is a string that reads the same forward or reversed.
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Objects;

public class NoToPalindromes {
	static int mod = 1000000007;

	static class Reader {
		final private int BUFFER_SIZE = 1 << 16;
		private DataInputStream din;
		private byte[] buffer;
		private int bufferPointer, bytesRead;

		public Reader() {
			din = new DataInputStream(System.in);
			buffer = new byte[BUFFER_SIZE];
			bufferPointer = bytesRead = 0;
		}

		public Reader(String file_name) throws IOException {
			din = new DataInputStream(new FileInputStream(file_name));
			buffer = new byte[BUFFER_SIZE];
			bufferPointer = bytesRead = 0;
		}

		public String readLine() throws IOException {
			byte[] buf = new byte[10005]; // line length
			int cnt = 0, c;
			while ((c = read()) != -1) {
				if (c == '\n')
					break;
				buf[cnt++] = (byte) c;
			}
			return new String(buf, 0, cnt);
		}

		public int nextInt() throws IOException {
			int ret = 0;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();
			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');

			if (neg)
				return -ret;
			return ret;
		}

		public long nextLong() throws IOException {
			long ret = 0;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();
			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');
			if (neg)
				return -ret;
			return ret;
		}

		public double nextDouble() throws IOException {
			double ret = 0, div = 1;
			byte c = read();
			while (c <= ' ')
				c = read();
			boolean neg = (c == '-');
			if (neg)
				c = read();

			do {
				ret = ret * 10 + c - '0';
			} while ((c = read()) >= '0' && c <= '9');

			if (c == '.') {
				while ((c = read()) >= '0' && c <= '9') {
					ret += (c - '0') / (div *= 10);
				}
			}

			if (neg)
				return -ret;
			return ret;
		}

		private void fillBuffer() throws IOException {
			bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
			if (bytesRead == -1)
				buffer[0] = -1;
		}

		private byte read() throws IOException {
			if (bufferPointer == bytesRead)
				fillBuffer();
			return buffer[bufferPointer++];
		}

		public void close() throws IOException {
			if (din == null)
				return;
			din.close();
		}
	}

	public static void main(String[] args) throws IOException {
		Reader in = new Reader();
		int i, t, n, p;
		n = in.nextInt();
		p = in.nextInt();
		in.readLine();
		String s = in.readLine().substring(0, n);
		if (p == 1 || (p == 2 && n > 2)) {
			System.out.println("NO");
			return;
		}
		if (p == 2 && n == 2) {
			String st = new String("ab");
			if (Objects.equals(s, st))
				System.out.println("ba");
			else
				System.out.println("NO");
			return;
		}
		char delimit = (char) (96 + p);
		if (n == 1 && p > 1) {
			if (s.charAt(0) == delimit)
				System.out.println("NO");
			else
				System.out.println((char) (s.charAt(0) + 1));
			return;
		}
		StringBuilder ans = new StringBuilder(s);

		boolean flag = true;

		for (i = n - 1; i >= 0; i--) {
//			if (s.charAt(i - 1) == s.charAt(i)) {
//				System.out.println("NO");
//				return;
//			}
//			if (i - 2 >= 0 && s.charAt(i - 2) == s.charAt(i)) {
//				System.out.println("NO");
//				return;
//			}
//			System.out.println("  i  " + i);
			flag = true;
			char orig = s.charAt(i), j;
			for (j = (char) (orig + 1); j <= delimit; j++) {
//				System.out.println(j + " *** " + i);
				boolean c1, c2;
				c1 = c2 = true;
				if ((i - 1) >= 0 && s.charAt(i - 1) == j)
					c1 = false;
				if ((i - 2) >= 0 && s.charAt(i - 2) == j)
					c2 = false;
				if (c1 && c2) {
					flag = false;
//					System.out.println(j + " " + i);
					ans.replace(i, i + 1, String.valueOf(j));
					String rep = getString(j, ans, n, i);
					for (int k = i + 1; k < (n / 3) * 3; k = k + 3)
						ans.replace(k, k + 3, rep);
					int y = n - i - 1;
					if (y % 3 == 0)
						break;
					else if (y % 3 == 1)
						y = 1;
					else if (y % 3 == 2)
						y = 2;
					for (int k = n - y, x = 0; k > i && k < n; k++) {
						ans.replace(k, k + 1, String.valueOf(rep.charAt(x)));
						x++;
					}
//					if (i + 1 < n && j == ans.charAt(i + 1))
//						ans.replace(i + 1, i + 2, "a");
//					else if (i + 2 < n && j == ans.charAt(i + 2))
//						ans.replace(i + 2, i + 3, "a");
					break;
				}
			}
			if (flag == false) {
				System.out.println(ans.substring(0, n));
				break;
			}
		}
		if (flag)
			System.out.println("NO");

	}

	private static String getString(char j, StringBuilder ans, int n, int i) {
		// TODO Auto-generated method stub
		String s = "abc";
		if (j == 'b') {
			if ((i - 1 >= 0 && ans.charAt(i - 1) != 'a') || i == 0)
				s = "acb";
			else if (i - 1 >= 0)
				s = "cab";
		} else if (j == 'a') {
			if ((i - 1 >= 0 && ans.charAt(i - 1) != 'b') || i == 0)
				s = "bca";
			else if (i - 1 >= 0)
				s = "cba";
		} else if (j == 'c') {
			if ((i - 1 >= 0 && ans.charAt(i - 1) != 'a') || i == 0)
				s = "abc";
			else if (i - 1 >= 0)
				s = "bac";
		} else {
			if (i - 1 >= 0 && ans.charAt(i - 1) == 'a')
				s = "bac";
			else
				s = "abc";

		}
		return s;
	}
}
