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 JavaScript (node.js v5.12) (judge verdict: Runtime Error)

let input = require('fs').readFileSync('/dev/stdin', 'utf8');

const data = input.split("\n");
const [peopleNum, flowTime] = data[0].split(' ');
const pushTimes = data[1].split(' ');

let rTime = 0;

for (let i = 0; i < parseInt(peopleNum, 10); i++) {
  const diffTime = i === 0 ? 0 : parseInt(pushTimes[i], 10) - parseInt(pushTimes[i - 1], 10);
  if (diffTime < parseInt(flowTime, 10) && diffTime !== 0) {
    rTime += diffTime;
  } else {
    rTime += parseInt(flowTime, 10);
  }
}

console.log(rTime);