program paletta; (*non funzionano come dovrebbero SOMMA E MODIFICA*)
var N,i0 ,i,z, dimpari, dimdispari:Longint;
V,pari, dispari, controllo: array of longint;
n_ribaltamenti,numero_ribaltamenti, piccolidopo,maggioriprima,fuoriposto, ricordafuoriposto:int64;
ordinabile: boolean;
function SOMMA(X:longint):int64;
begin
SOMMA:=0;
while (X >= 0) do
begin
SOMMA:=SOMMA+controllo[X];
X := (X and (X+1)) -1;
end
end;
Procedure modifica(X:longint; D:longint);
begin
while (X <D) do
begin
controllo[X]:=controllo[X]+1;
X := X or (X+1);
end
end;
function paletta_sort(N: longint; V: array of longint): int64;
begin
if N mod 2 = 0 then begin dimpari:=N div 2; dimdispari:= dimpari; end
else begin dimdispari:=N div 2 ; dimpari:= dimdispari+1; end;
Setlength(pari, dimpari+1);
Setlength(dispari, dimdispari+1);
Setlength(controllo, N);
for i:=0 to N-1 do if i mod 2 =0 then pari[i div 2 +1]:=V[i] div 2;
for i:=0 to N-1 do if i mod 2 <> 0 then dispari[i div 2 +1 ]:=(V[i] -1) div 2 ;
ordinabile:=true;
for z:=0 to N-1 do if V[z] mod 2 <> z mod 2 then begin ordinabile:=false; n_ribaltamenti:=-1; end;
if ordinabile=true then begin
for i:=0 to dimpari do controllo[i]:=0;
n_ribaltamenti:=0; piccolidopo:=0;
for i:=dimpari downto 1 do
begin
piccolidopo:=piccolidopo+somma(Pari[i]);
modifica (pari[i], dimpari);
end;
n_ribaltamenti:=n_ribaltamenti+piccolidopo;
for i:=0 to dimdispari do controllo[i]:=0;
piccolidopo:=0;
for i:=dimdispari downto 1 do
begin
piccolidopo:=piccolidopo+somma(Dispari[i]);
modifica (dispari[i], dimdispari);
end;
n_ribaltamenti:=n_ribaltamenti+piccolidopo;
end;
paletta_sort:=n_ribaltamenti;
end;
begin
(*assign(input, 'input.txt'); reset(input);
assign(output, 'output.txt'); rewrite(output);*)
{ Reading input }
readln( N);
Setlength(V, N);
for i0 := 0 to N-1 do
begin
read(V[i0]);
end;
{ Calling functions }
numero_ribaltamenti := paletta_sort(N, V);
{ Writing output }
writeln(numero_ribaltamenti);
end.
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