A delicious NxN grid is given to you. All the lattice points of this grid contain a cupcake each except for M specified points. (Those M points do not contain cupcakes.)
Now, you have to randomly choose four different lattice points from this grid. If your four chosen points make a rectangle and each of the four points contains a cupcake, then you will earn a cupcake for yourself.
Calculate the probability of winning a cupcake in the given grid.
First line contains two integers N (1 <= N <= 103) and M (0 <= M <= 50)
Each of next M lines contains two integers Xi(0 <= Xi <= N) and Yi(0 <= Yi <= N) describing the ith point where the cupcake is missing. (each of these points are distinct)
Print one number expressing the probability of earning a cupcake in following format. If the answer is P/Q, then print the number P ⋅ Q−1 modulo 109+7, where Q−1 denotes the multiplicative inverse of Q modulo 109+7.
2 1 1 1