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 Python (3.8.2) (judge verdict: Accepted)

#
# abc060 c
#
import sys
from io import StringIO
import unittest


class TestClass(unittest.TestCase):
    def assertIO(self, input, output):
        stdout, stdin = sys.stdout, sys.stdin
        sys.stdout, sys.stdin = StringIO(), StringIO(input)
        resolve()
        sys.stdout.seek(0)
        out = sys.stdout.read()[:-1]
        sys.stdout, sys.stdin = stdout, stdin
        self.assertEqual(out, output)

    def test_入力例_1(self):
        input = """2 4
0 3"""
        output = """7"""
        self.assertIO(input, output)

    def test_入力例_2(self):
        input = """2 4
0 5"""
        output = """8"""
        self.assertIO(input, output)

    def test_入力例_3(self):
        input = """4 1000000000
0 1000 1000000 1000000000"""
        output = """2000000000"""
        self.assertIO(input, output)

    def test_入力例_4(self):
        input = """1 1
0"""
        output = """1"""
        self.assertIO(input, output)

    def test_入力例_5(self):
        input = """9 10
0 3 5 7 100 110 200 300 311"""
        output = """67"""
        self.assertIO(input, output)


def resolve():
    N, T = map(int, input().split())
    t = list(map(int, input().split()))

    ans = T
    for i in range(N-2, -1, -1):
        ans += min(T, t[i+1]-t[i])

    print(ans)


if __name__ == "__main__":
    # unittest.main()
    resolve()