Support vector machine problem

Question

The support vector machine problem is described below: $$ \begin{aligned} \operatorname{min}_{w,b}&\frac{1}{2}||w||^2\\ \text{s.t. }& v^{(i)}(w^\top u^{(i)}+b)\geq 1,i=1,...,m \end{aligned} $$ By writing its dual problem, We can get the optimal solution of the dual $\lambda^*$. But how can I derive the primal optimal solution from the dual optimal solution?