program sample
    implicit none
    character(len=50)::O, E
    character(len=100)::cha
    character(len=1)::p, f
    character, allocatable::C(:)
    integer:: i
    read(*,*) O
    read(*,*) E
    allocate(C(len_trim(O)+len_trim(E)))
    cha = ''

    if(len_trim(O)>len_trim(E))then
        do i = 1, len_trim(O)-1
            C(2*i-1) = O(i:i)
            C(2*i) = E(i:i)
        end do
        C(len_trim(O)+len_trim(E)) = O(i:i)
    else
        do i = 1, len_trim(O)
            C(2*i-1) = O(i:i)
            C(2*i) = E(i:i)
        end do
    end if 

    write(*,*) C
    deallocate(C)
    stop

end program sample