   Program PanasonicB
   Implicit none
   Integer::i,j,k
 
      Read(*,*) i,j
      If (MOD(i,2)==0) then
         k=i*j/2
      Else
         If (MOD(j,2)==0) then
            k=(i-1)*j/2+j/2
         Else
            k=(i-1)*j/2+(j+1)/2
      End If
 
      Write(*,*) k
      Stop
 
   End Program PanasonicB