atcoder#ABC297F. [ABC297F] Minimum Bounding Box 2

[ABC297F] Minimum Bounding Box 2

Score : 500500 points

Problem Statement

We have a grid with HH rows and WW columns.

We choose KK cells in this grid uniformly at random. The score is the number of cells in the minimum rectangle (whose edges are parallel to the axes of the grid) that contains all of the chosen cells.

Find the expected score modulo 998244353998244353.

What is rational number modulo $998244353$?

We can prove that the sought expected value is always a rational number.
Moreover, under the Constraints of this problem, when the value is represented as \frac{P}{Q} by two coprime integers P and Q, we can prove that there is a unique integer R such that R \times Q \equiv P\pmod{998244353} and 0 \leq R \lt 998244353. Find such R.

Constraints

  • 1H,W10001\leq H,W \leq 1000
  • 1KHW1\leq K \leq HW
  • All values in the input are integers.

Input

The input is given from Standard Input in the following format:

HH WW KK

Output

Print the answer.

2 2 2
665496238

The score equals 44 in the following two cases: if cells (1,1)(1,1) and (2,2)(2,2) are chosen, or cells (1,2)(1,2) and (2,1)(2,1) are chosen. The other four cases yield a score of 22.

Thus, the expected score equals 4×2+2×46=83\frac{4 \times 2 + 2 \times 4} {6} = \frac{8}{3}. Since 665496238×38(mod998244353)665496238 \times 3 \equiv 8\pmod{998244353}, you should print 665496238665496238.

10 10 1
1
314 159 2653
639716353