# Arithmetic with large real numbers

I would like to manipulate arbitrarily large real numbers, for example:

```
a = 10**25+.1
round(a) # expected: 10000000000000000000000000
sage: 10000000000000000905969664
a.is_integer() # expected: False
sage: True
a - 10**25 # expected: 0.1
sage: 0.000000000000000
```

What is the appropriate function to use?