var a,i,s:longint; begin readln(a); s:=0; for i:=1 to a do s:=s+i; writeln(s); end.vara,i,s:longint;beginreadln(a);s:=0;for i:=1 to a dos:=s+i;writeln(s);end.

var a,i,s:longint; begin readln(a); s:=0; for i:=1 to a do s:=s+i; writeln(s); end.vara,i,s:longint;beginreadln(a);s:=0;for i:=1 to a dos:=s+i;writeln(s);end.
var a,i,s:longint; begin readln(a); s:=0; for i:=1 to a do s:=s+i; writeln(s); end.
var
a,i,s:longint;
begin
readln(a);
s:=0;
for i:=1 to a do
s:=s+i;
writeln(s);
end.

var a,i,s:longint; begin readln(a); s:=0; for i:=1 to a do s:=s+i; writeln(s); end.vara,i,s:longint;beginreadln(a);s:=0;for i:=1 to a dos:=s+i;writeln(s);end.
读入a,输出1~a的和.（等差数列）
以下源程序等同于以上程序：
var a:longint;
begin
readln(a);
writeln((1+a)*a div 2);
end.