Ответ:

program summa;

var sum, i, n:LongInt;

begin

ReadLn(n);

i:=1;

sum := 0;

while (i<=n) do

begin

sum:=sum+i;

i:=i+1;

end;

WriteLn(sum);

end.

===== PascalABC.NET =====

begin

 var n := ReadInteger('n =');

 var (i, s) := (1, 0);

 while i <= n do

 begin

   s += i;

   i += 1

 end;

 Print(s);

end.