Неправильный результат в методе Гаусса

uses  crt;
var
a:array[1..10,1..10]of real;
b:array[1..10] of real;
x:array[1..10] of real;
i,j,k,n:integer;
s,h:real;
{_________________________________________________________________________}
procedure sozd;
begin
writeln('Введите A[i,j]');
for i:=1 to n do  begin
for j:=1 to n do
read(a[i,j]);
end;
for i:=1 to n do
begin
for j:=1 to n do
write(a[i,j]:2:0);
writeln;
end;
begin
writeln('Введите B[i]');
for i:=1 to n do
read (b[i]);
end;
begin writeln('B=');
for i:=1 to n do
writeln (b[i]);
end;
end;
{_________________________________________________________________________}
procedure viv_mtr;//добавим процедуру вывода матрицы
begin
for i:=1 to n do
 begin
  for j:=1 to n do
  write(a[i,j]:2:0);
  writeln;
 end;
writeln;
readkey;
end;
{_________________________________________________________________________}
procedure perest;
var
z:integer;
f:real;
begin
if a[k+1,k]<>0 then
for z:=k to n do
begin
f:=a[k,z];
a[k,z]:=a[k+1,z];
a[k+1,z]:=f
end
end;
{________________________________________________________________________}
procedure Gaussa;
begin
for k:=1 to n-1 do
 begin
  if a[k,k]<>0 then
   begin
    b[k]:=b[k]/a[k,k];
    for j:=n downto 1 do
    a[k,j]:=a[k,j]/a[k,k];
    for i:=k to n-1 do
     begin
      h:=a[i+1,k];
      for j:=k to n do
      a[i+1,j]:=a[k,j]*((-1)*h)+a[i+1,j];
      b[i+1]:=b[k]*((-1)*h)+b[i+1];
     end;
   end
  else perest;
  viv_mtr;//после каждого преобразования вывод
if a[n,n]=0 then
x[n]:=0
else
x[n]:=b[n]/a[n,n];
for i:=n-1 downto 1 do
begin
s:=0;
for j:=n downto i+1 do
s:=a[i,j]*x[j]+s;
x[i]:=(-1)*s+b[i]
end
end;
end;
 {_______________________________________________________________________}
procedure vivod;
begin
writeln('Korni uravneniya');
for i:=1 to n do
writeln('x',i,'=',x[i]:0:5)
end;
 {_________________________________________________________________________}
begin
clrscr;
writeln('Vvedite razmernost:');
readln(n);
sozd;
writeln;
Gaussa;
writeln;
vivod;
readkey
end.