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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
class Program{
    static void Main(string[] args){
        string[] nt = Console.ReadLine().Split(' ');
        int n = int.Parse(nt[0]);
        int t = int.Parse(nt[1]);
        string[] tempT = Console.ReadLine().Split(' ');
        int[] time = new int[tempT.Length];
        for(int i=0;i<time.Length;i++){
            time[i] = int.Parse(tempT[i]);
        }
        int amount = 0;
        int timeline = 0;
        for(int i=0;i<time.Length;i++){
            if(i == time.Length - 1){
                amount += t;
                break;
            }
            if(timeline + t > timeline + time[i+1]){
                amount +=  time[i+1] - time[i];
                timeline += t;
            }else{
                amount += t;
                timeline += t;
            }
        }
        Console.WriteLine(amount);
    }
}