program prob2
    implicit none
    integer::n, i
    integer(16)::l(0:86)
    l(0) = 2
    l(1) = 1
    do i = 2, 86
        l(i) = l(i-1) + l(i-2)
    end do
    read(*,*) n
    write(*,*) l(n)
    stop
end program