#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) {

  auto tateSum = make_v< int >(H + 1, W, 26);
  for(int i = 0; i < H; i++) {
    for(int j = 0; j < W; j++) {
      tateSum[i + 1][j][S[i][j]]++;
      for(int k = 0; k < 26; k++) {
        tateSum[i + 1][j][k] += tateSum[i][j][k];
      }
    }
  }
  auto yokoSum = make_v< int >(H, W + 1, 26);
  for(int i = 0; i < H; i++) {
    for(int j = 0; j < W; j++) {
      yokoSum[i][j + 1][S[i][j]]++;
      for(int k = 0; k < 26; k++) {
        yokoSum[i][j + 1][k] += yokoSum[i][j][k];
      }
    }
  }

  auto tate = [&](int idx, int l, int r) {
    int add = 0;
    for(int k = 0; k < 26; k++) {
      if(yokoSum[idx][r][k] - yokoSum[idx][l][k] > 0) {
        add |= 1 << k;
      }
    }
    return add;
  };

  auto yoko = [&](int idx, int l, int r) {
    int add = 0;
    for(int k = 0; k < 26; k++) {
      if(tateSum[r][idx][k] - tateSum[l][idx][k] > 0) {
        add |= 1 << k;
      }
    }
    return add;
  };


  int64 ans = 0;

  for(int top = 0; top < H; top++) {
    for(int left = 0; left < W; left++) {
      int mask = 0;
      for(int len = 1; top + len <= H && left + len <= W; len++) {
        mask |= tate(top + len - 1, left, left + len);
        mask |= yoko(left + len - 1, top, top + len);
        if(__builtin_popcount(mask) == K)++ans;
      }
    }
  }

  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;
}