Как поменять местами минимальный и первый элемент матрицы в паскале?

var
a: array [1..5, 1..4] of integer;
mi, mj, t, i, j: integer;
begin
randomize;
writeln('matrix:');
for i := 1 to 5 do begin
for j := 1 to 4 do begin
a[i, j] := random(100);
write(a[i, j]:4);
end;
writeln;
end;
mi := 1;
mj := 1;
for i := 1 to 5 do
for j := 1 to 4 do
if a[i, j] < a[mi, mj] then begin
mi := i;
mj := j;
end;
t := a[1, 1];
a[1, 1] := a[mi, mj];
a[mi, mj] := t;
writeln('result:');
for i := 1 to 5 do begin
for j := 1 to 4 do write(a[i, j]:4);
writeln;
end;
end.