Can anyone give me any suggestion of how to solve this integral? Or better - has anyone seen any solution to this kind of integral?

$\displaystyle

\int_0^1\int_0^1\cdots \int_0^1\frac{1}{\left( c+x_{1}+x_{2}+\cdots +x_{n}\right) }dx_{1}\cdots dx_{n}

$

I would be grateful for any help!