SPOJ Problem Set (classical)
4329. Counting KRectangle
Problem code: KRECT

Given a M*N square board. Each square contains a letter of the English alphabet ('A' .. 'Z').
A Krectangle of the board is a rectangle whose sides are parallel to the sides of the board, and contains exactly K different types of letter.
For example, with this 4*3 board:
CED
CEB
CBC
DDA
The rectangle [(1,1), (2,2)] is a 2rectangle of the board because it contains 2 different letters: C and E.
Given M, N, K and the M*N board. Determine how many Krectangles there are in the board.
Input
The first line contains 3 integers M, N and K. (1 ≤ M, N ≤ 100, 1 ≤ K ≤ 26)
The following M lines, each contains N letters of the English alphabet ('A' .. 'Z')
Output
Write one integer  the number of Krectangles in the given board.
Example
Input:
4 3 3
CED
CEB
CBC
DDA
Output:
12
