function opred(var c:aa;n:integer):real;
var i,j,k,ac,h:integer;
    b:aa;
    y:real;
begin
if n=2 then opred:=c[1,1]*c[2,2]-c[1,2]*c[2,1] else begin
y:=0; for i:=1 to n do begin
for j:=2 to n do begin
k:=1;
for h:=1 to n do if h<>i then begin b[j-1,k]:=c[j,h]; k:=k+1; end;
end;
ac:=-1; for h:=1 to i do ac:=ac*(-1);
y:=y+ac*c[1,i]*opred(b,n-1);
end;
opred:=y;
end;end;