\[\boxed{\mathbf{1376}.}\]
\[\angle ABC = 180{^\circ}.\]
\[\angle ABM + \angle KBC =\]
\[= 180{^\circ} - 90{^\circ} = 90{^\circ};\]
\[\angle ABM = 90{^\circ}\ :2 = 45{^\circ}.\]
\[Ответ:45{^\circ}.\]