Условие: найти сумму элементов двумерного массива

const
 m = 5;
 n = 4;
 
var
 a: array[1..m,1..n] of byte;
 s: array[1..n] of byte;
 i,j, sum: byte;
 
begin
 randomize;
 
 for i := 1 to m do begin
 for j := 1 to n do begin
 a[i,j] := random(10);
 write (a[i,j]:3)
 end;
 writeln
 end;
 
 writeln ('------------');
 
 for j := 1 to n do begin
 for i := 1 to m do begin
 s[j] := s[j] + a[i,j];
 sum := sum + a[i,j]
 end;
 write (s[j]:3)
 end;
 
 write (' | sum = ', sum);
 
readln
end.