PROGRAMMING:Body mass index (exercise 6-3, fundamentals and applications of Python programming, Higher Education Society)

Body mass index (BMI) is the square of weight divided by height. Weight in kg, height
The unit is meter. BMI is a commonly used international standard to measure the degree of obesity and health. Here's the BMI chart for people over 16
Table:
|BMI | explanation|
| :--------: | :--: |
|BMI < 18 | ultra light|
|18 < = BMI < 25 | standard|
|25 < = BMI < 27 | overweight|
|27 < = BMI | obesity|
Write a program, input user's weight (kg) and height (m), display their BMI value, and make explanatory evaluation.
###Input format:
Weight, height
###Output format:
Ultra light / standard / overweight / obesity.
###Input example:
```in
70,1.75
```
###Output example:
```out
standard
```







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