import java.awt.geom.Point2D;
import java.io.*;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;
import java.util.Scanner;

public class Main {

	static final PrintWriter out = new PrintWriter(System.out);
	static final FastScanner sc = new FastScanner();
	static final Scanner stdIn = new Scanner(System.in);
	public static void main(String[] args) {
		int n = sc.nextInt();
		int l = sc.nextInt();
		int[] list = new int[n];
		for(int i = 0; i < n; i++) {
			list[i] = sc.nextInt();
		}
		int count = 0;
		int time  = 0;
		PriorityQueue<Data> ar1 = new PriorityQueue<Data>();
		ArrayList<Integer> t = new ArrayList<Integer>();
		if(list[0] > list[1]) ar1.add(new Data(0,list[0]));
		if(list[n-1] > list[n-2]) ar1.add(new Data(n-1,list[n-1]));
		if(n > 2)
			for(int i = 1; i < n-1; i++) {
				if(list[i] > list[i-1] && list[i] > list[i+1]) ar1.add(new Data(i,list[i]));
			}
		while(!ar1.isEmpty()) {
			Data tmp = ar1.poll();
			int plus =  l - (tmp.len + time);
			if(plus > 0) {
				time += plus;
			}
			list[tmp.id] = 0;
			count++;
			if(tmp.id != 0) {
				if(tmp.id - 2 >= 0) {
					if(list[tmp.id-1] >= list[tmp.id-2] && list[tmp.id-1] != 0) ar1.add(new Data(tmp.id-1,list[tmp.id-1] - time));
				}
				else {
					if(list[tmp.id-1] != 0) ar1.add(new Data(tmp.id-1,list[tmp.id-1] - time));
				}
			}
			if(tmp.id != n-1) {
				if(tmp.id + 2 <= n-1) {
					if(list[tmp.id+1] >= list[tmp.id+2] && list[tmp.id+1] != 0) ar1.add(new Data(tmp.id+1,list[tmp.id+1] - time));
				}
				else {
					if(list[tmp.id+1] != 0) ar1.add(new Data(tmp.id+1,list[tmp.id+1] - time));
				}
			}
		}
		System.out.println(time);






	}
	static class Data implements Comparable<Data> {
		int id;
		int len;

		Data(int a, int b) {
			id = a;
			len = b;
		}

		@Override
		public int compareTo(Data o) {
			return o.len - this.len;
		}

	}





}

//------------------------------//
//-----------//
class FastScanner {
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;
	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		}else{
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}
	private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
	private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
	private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;}
	public boolean hasNext() { skipUnprintable(); return hasNextByte();}
	public String next() {
		if (!hasNext()) throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while(isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}
	public long nextLong() {
		if (!hasNext()) throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){
				return minus ? -n : n;
			}else{
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

	public int nextInt() {
		if (!hasNext()) throw new NoSuchElementException();
		int n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while(true){
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			}else if(b == -1 || !isPrintableChar(b)){
				return minus ? -n : n;
			}else{
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}

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


}

Measured memory_bytes: 31728