uses crt;
var n,i,t:integer;
begin
clrscr;
write('n='); readln(n);
t:=0;
for i:=0 to n-1 do
t:=t+i;
writeln('tong cua ',n,' so tu nhien dau tien la: ',t);
readln;
end.
uses crt;
var n,i,t:integer;
begin
clrscr;
write('n='); readln(n);
t:=0;
for i:=0 to n-1 do
t:=t+i;
writeln('tong cua ',n,' so tu nhien dau tien la: ',t);
readln;
end.