params = {'depth':[3,1,2,6,4,5,7,8,9,10],
          'iterations':[250,100,500,1000],
          'learning_rate':[0.03,0.001,0.01,0.1,0.2,0.3], 
          'l2_leaf_reg':[3,1,5,10,100],
          'border_count':[32,5,10,20,50,100,200],
          'ctr_border_count':[50,5,10,20,100,200],
          'thread_count':4}