You are given two ints: n and m.
Let D[i] be the number of permutations of the set {1,2,...,n+i} such that the first i values are not fixed points of the permutation.
Formally, we are interested in permutations p such that for each j between 1 and i, inclusive, we have p(j) != j.
Next, let B[i] = (D[i] / n!) modulo (10^9 + 7).
Note that it can be shown that D[i] divided by n! is always an integer.
Compute and return the bitwise xor of the values B[i] for i between 1 and m, inclusive.
