Before revision:  We note that ratio \alpha  -\epsilon can be achieved using  {(1/\epsilon)}^{O(1/\epsilon^4)}n\log n value oracle calls, but this algorithm is impractical already for large } values of \epsilon.
After revision:  We note that ratio \alpha -\epsilon )-approximation. However, the algorithm of Ene {(1/\epsilon)}^{O(1/\epsilon^4)}n\log n value oracle calls, but this algorithm is impractical already for large } values of \epsilon.