Python 2 (13 chars)

Not sure if this is allowed:

exec(input())

Example of usage:

Input: 'print "Hello World!"'

Output: Hello World!

Python 2 (13 chars)

Not sure if this is allowed:

exec(input())

Example 1:

Input: 'print "Hello World!"'

Output: Hello World!

Example 2:

Input: 'import math; print math.pi'

Output: 3.14159265359