import java.io.*; import java.util.*; public class Main_yukicoder866_1 { private static Scanner sc; private static Printer pr; private static void solve() { int h = sc.nextInt(); int w = sc.nextInt(); int k = sc.nextInt(); char[][] c = new char[h][]; for (int i = 0; i < h; i++) { c[i] = sc.next().toCharArray(); } int[][][] cnt = new int[26][h + 1][w + 1]; for (char cc = 'a'; cc <= 'z'; cc++) { int cci = cc - 'a'; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { if (c[i][j] == cc) { cnt[cci][i + 1][j + 1]++; } } } for (int i = 0; i <= h; i++) { for (int j = 0; j <= w; j++) { if (i > 0) { cnt[cci][i][j] += cnt[cci][i - 1][j]; } if (j > 0) { cnt[cci][i][j] += cnt[cci][i][j - 1]; } if (i > 0 && j > 0) { cnt[cci][i][j] -= cnt[cci][i - 1][j - 1]; } } } } int ans = 0; for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { int ik = 0, ik1 = 0; { int l = 0; int r = Math.min(h - i, w - j) + 1; while (r - l > 1) { int mid = l + (r - l) / 2; if (f(mid, cnt, i, j) >= k) { // if (data[mid] >= value) { r = mid; } else { l = mid; } } // return r; ik = r; } { int l = 0; int r = Math.min(h - i, w - j) + 1; while (r - l > 1) { int mid = l + (r - l) / 2; if (f(mid, cnt, i, j) >= k + 1) { // if (data[mid] >= value) { r = mid; } else { l = mid; } } // return r; ik1 = r; } int tmp = ik1 - ik; ans += tmp; } } pr.println(ans); } private static Map hm; private static int pi = -1; private static int pj = -1; private static int f(int mid, int[][][] cnt, int i, int j) { if (pi != i || pj != j) { hm.clear(); pi = i; pj = j; } Integer tmp1 = hm.get(mid); if (tmp1 != null) { return tmp1; } int tmp = 0; for (int cci = 0; cci < 26; cci++) { int tmp2 = cnt[cci][i + mid - 1 + 1][j + mid - 1 + 1] - cnt[cci][i + mid - 1 + 1][j - 1 + 1] - cnt[cci][i - 1 + 1][j + mid - 1 + 1] + cnt[cci][i - 1 + 1][j - 1 + 1]; if (tmp2 > 0) { tmp++; } } hm.put(mid, tmp1); return tmp; } // --------------------------------------------------- public static void main(String[] args) { sc = new Scanner(System.in); pr = new Printer(System.out); solve(); pr.close(); sc.close(); } static class Scanner { BufferedReader br; Scanner (InputStream in) { br = new BufferedReader(new InputStreamReader(in)); } private boolean isPrintable(int ch) { return ch >= '!' && ch <= '~'; } private boolean isCRLF(int ch) { return ch == '\n' || ch == '\r' || ch == -1; } private int nextPrintable() { try { int ch; while (!isPrintable(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } return ch; } catch (IOException e) { throw new NoSuchElementException(); } } String next() { try { int ch = nextPrintable(); StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (isPrintable(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } int nextInt() { try { // parseInt from Integer.parseInt() boolean negative = false; int res = 0; int limit = -Integer.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Integer.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } int multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } long nextLong() { try { // parseLong from Long.parseLong() boolean negative = false; long res = 0; long limit = -Long.MAX_VALUE; int radix = 10; int fc = nextPrintable(); if (fc < '0') { if (fc == '-') { negative = true; limit = Long.MIN_VALUE; } else if (fc != '+') { throw new NumberFormatException(); } fc = br.read(); } long multmin = limit / radix; int ch = fc; do { int digit = ch - '0'; if (digit < 0 || digit >= radix) { throw new NumberFormatException(); } if (res < multmin) { throw new NumberFormatException(); } res *= radix; if (res < limit + digit) { throw new NumberFormatException(); } res -= digit; } while (isPrintable(ch = br.read())); return negative ? res : -res; } catch (IOException e) { throw new NoSuchElementException(); } } float nextFloat() { return Float.parseFloat(next()); } double nextDouble() { return Double.parseDouble(next()); } String nextLine() { try { int ch; while (isCRLF(ch = br.read())) { if (ch == -1) { throw new NoSuchElementException(); } } StringBuilder sb = new StringBuilder(); do { sb.appendCodePoint(ch); } while (!isCRLF(ch = br.read())); return sb.toString(); } catch (IOException e) { throw new NoSuchElementException(); } } int[] nextIntArray(int n) { int[] ret = new int[n]; for (int i = 0; i < n; i++) { ret[i] = sc.nextInt(); } return ret; } int[][] nextIntArrays(int n, int m) { int[][] ret = new int[m][n]; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { ret[j][i] = sc.nextInt(); } } return ret; } void close() { try { br.close(); } catch (IOException e) { // throw new NoSuchElementException(); } } } static class Printer extends PrintWriter { Printer(OutputStream out) { super(out); } void printInts(int... a) { StringBuilder sb = new StringBuilder(32); for (int i = 0, size = a.length; i < size; i++) { if (i > 0) { sb.append(' '); } sb.append(a[i]); } println(sb); } void printLongs(long... a) { StringBuilder sb = new StringBuilder(64); for (int i = 0, size = a.length; i < size; i++) { if (i > 0) { sb.append(' '); } sb.append(a[i]); } println(sb); } void printStrings(String... a) { StringBuilder sb = new StringBuilder(32); for (int i = 0, size = a.length; i < size; i++) { if (i > 0) { sb.append(' '); } sb.append(a[i]); } println(sb); } } }