Which mountain peak is also known as K-4 ?

Which mountain peak is also known as K-4 ?

Explanation

K1 is known as Masherbrum

K3 as Gasherbrum IV

K4 as Gasherbrum IIĀ 

K5 as Gasherbrum I.

Only K2, the second highest mountain in the world, has retained Montgomerie's name.