题目描述
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-----
2 4
0 3
-----Sample Output-----
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.
输入格式
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输出格式
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