Given a string, swap the case for each of the letters.
e.g. CodEwArs --> cODeWaRS
### Examples
```
""           ->   ""
"CodeWars"   ->   "cODEwARS"
"abc"        ->   "ABC"
"ABC"        ->   "abc"
"123235"     ->   "123235"
```
def swap(string_):
    return string_.swapcase()
def swap(string_):
    return string_.swapcase()