#include <bits/stdc++.h>
using namespace std;

int main() {
  ios::sync_with_stdio(false);

  int H, W, K;
  cin >> H >> W >> K;

  vector<string> G(H);
  for (int i = 0; i < H; ++i) {
    cin >> G[i];
  }

  int ans = 0;
  vector<vector<vector<int>>> dp(2, vector<vector<int>>(H, vector<int>(W)));
  for (int l = 1; l <= min(H, W); ++l) {
    for (int i = 0; i + l <= H; ++i) {
      for (int j = 0; j + l <= W; ++j) {
        dp[l & 1][i][j] = 1 << G[i][j] - 'a';
        if (1 < l) {
          dp[l & 1][i][j] |= 1 << G[i + l - 1][j + l - 1] - 'a';
          dp[l & 1][i][j] |= dp[~l & 1][i + 1][j];
          dp[l & 1][i][j] |= dp[~l & 1][i][j + 1];
        }
        ans += __builtin_popcount(dp[l & 1][i][j]) == K;
      }
    }
  }

  cout << ans << endl;

  return 0;
}