write a program to sum the main diagonal of a matrices (find the trace of a matrices)

implicit double precision (a-h,o-z)
    dimension A(3,3)
    DATA A/1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0/
    C=0
    do i=1,3
    j=i   
    C=C+A(i,j)
    enddo
    write(*,*)C
    stop
    end