package main

import (
	"bufio"
	"os"
	"strconv"
)

func main() {
	in := bufio.NewScanner(os.Stdin)
	in.Split(bufio.ScanWords)
	in.Buffer(make([]byte, 1024), 1<<20)

	nextInt := func() int {
		in.Scan()
		v, _ := strconv.Atoi(in.Text())
		return v
	}
	nextStr := func() string {
		in.Scan()
		return in.Text()
	}

	n := nextInt()
	m := nextInt()
	k := nextInt()

	grid := make([][]byte, n)
	for i := 0; i < n; i++ {
		grid[i] = []byte(nextStr())
	}

	if n > m {
		t := make([][]byte, m)
		for j := 0; j < m; j++ {
			row := make([]byte, n)
			for i := 0; i < n; i++ {
				row[i] = grid[i][j]
			}
			t[j] = row
		}
		grid = t
		n, m = m, n
	}

	var ans int64
	var countA [400]int
	var prefix [401]int
	var pos [26][400]int
	var plen [26]int

	for top := 0; top < n-1; top++ {
		topRow := grid[top]
		for c := 0; c < m; c++ {
			if topRow[c] == 'a' {
				countA[c] = 1
			} else {
				countA[c] = 0
			}
		}

		for bottom := top + 1; bottom < n; bottom++ {
			botRow := grid[bottom]

			for i := 0; i < 26; i++ {
				plen[i] = 0
			}

			prefix[0] = 0
			for c := 0; c < m; c++ {
				if botRow[c] == 'a' {
					countA[c]++
				}
				prefix[c+1] = prefix[c] + countA[c]
				if topRow[c] == botRow[c] {
					idx := int(topRow[c] - 'a')
					pos[idx][plen[idx]] = c
					plen[idx]++
				}
			}

			for ch := 0; ch < 26; ch++ {
				l := plen[ch]
				if l < 2 {
					continue
				}
				arr := pos[ch][:l]
				p := 0
				for j := 0; j < l; j++ {
					thr := prefix[arr[j]+1] - k
					for p < j && prefix[arr[p]] < thr {
						p++
					}
					ans += int64(j - p)
				}
			}
		}
	}

	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	out.WriteString(strconv.FormatInt(ans, 10))
	out.Flush()
}