A9578 | Dreamoon and Sums

Dreamoon loves summing up something for no reason. One day he obtains two integers $a$ and $b$ occasionally. He wants to calculate the sum of all nice integers. Positive integer $x$ is called nice if  and , where $k$ is some integer number in range $\[1,a\]$ .

By  we denote the quotient of integer division of $x$ and $y$ . By  we denote the remainder of integer division of $x$ and $y$ . You can read more about these operations here: http://goo.gl/AcsXhT.

The answer may be large, so please print its remainder modulo $1000000007$ ( $10^{9}+7$ ). Can you compute it faster than Dreamoon?

The single line of the input contains two integers $a$ , $b$ ( $1<=a,b<=10^{7}$ ).

Print a single integer representing the answer modulo $1000000007$ ( $10^{9}+7$ ).