[求助] 求大神指导error #6637

PROGRAM MAIN
   REAL W(5,5)
   CALL READIN(W)
   CALL PUTOUT(W)
  CALL WMAX(W,X1,X2) !// 此行出问题
   WRITE(*,*)'X1=',X1,'X2=',X2
    END

    SUBROUTINE READIN(A)
    REAL A(5,5)
    WRITE(*,*)'Enter 5*5 matrix:'
    DO 10 I=1,5
        READ(*,*)(A(I,J),J=1,5)
10  CONTINUE
    END

    SUBROUTINE PUTOUT(A)
    REAL A(5,5)
    DO 20 I=1,5
        WRITE(*,*) (A(I,J),J=1,5)
20  CONTINUE
    END

    SUBROUTINE WMAX(A,S1,S2)
    S1=A(1,1)
    S2=A(1,5)
    DO 30 I=2,5
        IF(S1.LT.A(I,I)) S1=A(I,I)
        IF(s2.LT.A(I,5-I+1)) S2=A(I,5-I+1)
30  CONTINUE
    END

SUBROUTINE WMAX(A,S1,S2)
  Real A(5,5) !// 添加此句
    S1=A(1,1)

Program main
  Implicit None !// 很重要
  Real w(5, 5) , x1 , x2
  Call readin(w)
  Call putout(w)
  Call wmax(w, x1, x2)
  Write (*, *) 'X1=', x1, 'X2=', x2

contains

Subroutine readin(a)
  Implicit None !// 很重要
  Real a(:,:)
  integer :: i
  Write (*, *) 'Enter 5*5 matrix:'
  Do i = 1, size(a,dim=1)
    Read (*, *) a(i,:)
  End Do
End Subroutine readin

Subroutine putout(a)
  Implicit None !// 很重要
  Real a(:, :)
  integer :: i
  Do i = 1, size(a,dim=1)
    Write (*, *) a(i,:)
  End Do
End Subroutine putout

Subroutine wmax(a, s1, s2)
  Implicit None !// 很重要
  Real a(:, :) , s1 , s2
  integer :: i , N
  N = size(a,dim=2)
  s1 = a(1, 1)
  s2 = a(1, N)
  Do i = 2, N
    If (s1<a(i,i)) s1 = a(i, i)
    If (s2<a(i,N-i+1)) s2 = a(i, N-i+1)
  End Do
End Subroutine wmax

End Program main