var
a, b, c, i, sum : integer;
begin
read (a, b, c);
sum := 0;
for i := b to c do inc (sum, i);
writeln (sum);
end.
var
a, b, c, i, sum : integer;
begin
read (a, b, c);
sum := 0;
for i := b to c do inc (sum, i);
writeln (sum);
end.