program sigma_mn
implicit none
integer i, m, n, wa
n = 0
m = 0
write(*, '(a)', advance = 'no')'input n :'
read (* ,*) n
write(*, '(a)', advance = 'no')'input m :'
read (* ,*) m
wa = 0
do i = m, n
wa = wa + i
enddo
write(*, *)'wa = ', wa
end program sigma_mn
