#include <bits/stdc++.h>

using namespace std;

using int64 = long long;
const int mod = 1e9 + 7;

const int64 infll = (1LL << 62) - 1;
const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;


template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 > &p) {
  os << p.first << " " << p.second;
  return os;
}

template< typename T1, typename T2 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for(int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for(T &in : v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for(auto &e : t) fill_v(e, v);
}

template< typename F >
struct FixPoint : F {
  FixPoint(F &&f) : F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}


int64 solve(vector< string > &S, int H, int W, int K) {

  vector< vector< vector< int > > > uku(H, vector< vector< int > >(W));

  for(int top = 0; top < H; top++) {
    for(int left = 0; left < W; left++) {
      for(int len = 1; top + len <= H && left + len <= W; len++) {
        uku[top][left].emplace_back(0);
      }
    }
  }

  for(int m = 0; m < 26; m++) {

    auto tateSum = make_v< short >(H + 1, W);
    for(int i = 0; i < H; i++) {
      for(int j = 0; j < W; j++) {
        if(S[i][j] == m) tateSum[i + 1][j]++;
        tateSum[i + 1][j] += tateSum[i][j];
      }
    }
    auto yokoSum = make_v< short >(H, W + 1);
    for(int i = 0; i < H; i++) {
      for(int j = 0; j < W; j++) {
        if(S[i][j] == m) yokoSum[i][j + 1]++;
        yokoSum[i][j + 1] += yokoSum[i][j];
      }
    }

    auto tate = [&](int idx, int l, int r) {
      return yokoSum[idx][r] - yokoSum[idx][l] > 0;
    };

    auto yoko = [&](int idx, int l, int r) {
      return tateSum[r][idx] - tateSum[l][idx] > 0;
    };

    for(int top = 0; top < H; top++) {
      for(int left = 0; left < W; left++) {
        int mask = 0;
        for(int len = 1, p = 0; top + len <= H && left + len <= W; len++, p++) {
          mask |= tate(top + len - 1, left, left + len);
          mask |= yoko(left + len - 1, top, top + len);
          if(mask)uku[top][left][p]++;
        }
      }
    }

  }

  int64 ans = 0;

  for(int top = 0; top < H; top++) {
    for(int left = 0; left < W; left++) {
      int mask = 0;
      for(auto &p : uku[top][left]) ans += p == K;
    }
  }
  return ans;
}


int main() {
  int H, W, K;
  cin >> H >> W >> K;
  vector< string > S(H);
  cin >> S;
  for(auto &c : S) for(auto &t : c) t -= 'a';
  cout << solve(S, H, W, K) << endl;
}