C1:Var S,i,n:Longint;
begin
Readln(n)
S:=0;
For i:=1 to n do S:=S+i;
Write('Tong cac so tu 1 den n : ',S);
Readln;
End.
C2:Var i,S,n:Longint;
begin
Readln(n)
i:=1; S:=0;
while i<=n do
begin
S:=S+i;
i:=i+1;
end;
write('Tong cac so tu 1 den n: ',S);
Readln;
End.