Problem:
Score : 300 points

Problem Statement

In a public bath, there is a shower which emits water for T seconds when the switch is pushed.

If the switch is pushed when the shower is already emitting water, from that moment it will be emitting water for T seconds.
Note that it does not mean that the shower emits water for T additional seconds.

N people will push the switch while passing by the shower.
The i-th person will push the switch t_i seconds after the first person pushes it.

How long will the shower emit water in total?

Constraints

1 ≤ N ≤ 200,000

1 ≤ T ≤ 10^9

0 = t_1 < t_2 < t_3 < , ..., < t_{N-1} < t_N ≤ 10^9

T and each t_i are integers.

Input

Input is given from Standard Input in the following format:

N T
t_1 t_2 ... t_N

Output

Assume that the shower will emit water for a total of X seconds. Print X.

Sample Input 1

2 4
0 3

Sample Output 1

7

Three seconds after the first person pushes the water, the switch is pushed again and the shower emits water for four more seconds, for a total of seven seconds.

Sample Input 2

2 4
0 5

Sample Output 2

8

One second after the shower stops emission of water triggered by the first person, the switch is pushed again.

Sample Input 3

4 1000000000
0 1000 1000000 1000000000

Sample Output 3

2000000000

Sample Input 4

1 1
0

Sample Output 4

1

Sample Input 5

9 10
0 3 5 7 100 110 200 300 311

Sample Output 5

67

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;
import java.io.*;
//import java.util.stream.Stream;
import static java.lang.Math.*;

public class Main {
	Scanner cin;

	void init() throws Exception {
		cin = new Scanner(new BufferedInputStream(System.in));
//		cin = new Scanner(new File("in.txt"));
//		System.setOut(new PrintStream(new File("out.txt")));
		solve();
	}

	void solve() {
		int N = cin.nextInt();
		int T = cin.nextInt();
		int[] t = new int[N];
		int cnt = 0;
		t[0] = cin.nextInt();
		for (int i=1;i<N;i++){
			t[i] = cin.nextInt();
			cnt += min(t[i]-t[i-1], T);
		}
		cnt += T;
		System.out.println(cnt);
	}

	public static void main(String[] args) throws Exception {
		Main M = new Main();
		M.init();
	}

}