a,
var n, i: integer; S: real;
begin
read(n);
while i <= n do
begin
S:=S+i*(i+1);
i:=i+1;
end;
write(S);
end.
b,
var n,i: integer; S: real;
begin
read(n);
while i <= n do
begin
S:=S+2*i;
i:=i+1;
end;
write(S);
end.
c,
var n,i: integer; S: real;
begin
read(n);
while i <=n do
begin
S:=S+(2*i+1);
i:=i+1;
end;
write(S);
end.
T CHỊU