Proving $\sum_{k=0}^{n}k{n\choose k} = n{2n-1 \choose n-1} $

Proving $\sum_{k=0}^{n}k{n\choose k} = n{2n-1 \choose n-1} $

I'm struggling at proving the following combinatorical identity:
$$\sum_{k=0}^{n}k{n\choose k} = n{2n-1 \choose n-1} $$ I would like to see
a combinatorical (logical) solution, or an algebraic solution.