PROGRAMMING:Lighting
There are n cowsheds in the cattle farm, numbered from 1 to n. a lamp is installed in front of each cowshed, and K lamps have been turned on at present. In order to ensure the lighting at night, it is required that at least two lights should be lit in each continuous cowshed. How many lights should be lit at least?
###Input format:
Enter the first line of three integers n, K, R (2 = < n < = 100000, 0 = < K < = n, 0 = < R < = n), representing the number of cowsheds, the number of lights that have been lit, and the number of continuous cowshed required by the topic; Then K lines, each line is an integer, representing the cowshed number of the lit K lights.
###Output format:
Output in order to ensure the continuous R cowshed at least two lights are lit, at least the number of lights that need to be lit.
###Input example:
```in
15 5 4
two
five
seven
ten
thirteen
```
###Output example:
```out
three
```
answer：If there is no answer, please comment
###Input format:
Enter the first line of three integers n, K, R (2 = < n < = 100000, 0 = < K < = n, 0 = < R < = n), representing the number of cowsheds, the number of lights that have been lit, and the number of continuous cowshed required by the topic; Then K lines, each line is an integer, representing the cowshed number of the lit K lights.
###Output format:
Output in order to ensure the continuous R cowshed at least two lights are lit, at least the number of lights that need to be lit.
###Input example:
```in
15 5 4
two
five
seven
ten
thirteen
```
###Output example:
```out
three
```
answer：If there is no answer, please comment