program prob27
    implicit none
    integer :: a,b,c
    write(*,*) a,b,c
    if(a <= c .and. b <= c) then
        write(*,*) a * b / 2
    else if(a <= b .and. c <= b) then
        write(*,*) a*c/2
    else
        write(*,*) b*c/2
    end if

    stop
contains
end program prob27