#include <bits/stdc++.h>
using namespace std;
template <typename _T>
inline void _DBG(const char *s, _T x) {
  cerr << s << " = " << x << "\n";
}
template <typename _T, typename... args>
void _DBG(const char *s, _T x, args... a) {
  while (*s != ',') cerr << *s++;
  cerr << " = " << x << ',';
  _DBG(s + 1, a...);
}
const int N = 307;
int n, m, p[] = {1, 0, 0, 1, -1, 0, 0, -1};
char s[N][N];
long long P, q;
long long val[N][N];
queue<pair<pair<int, int>, long long> > Q;
bool vis[N][N];
vector<pair<int, int> > kto;
void bfs(int x, int y, long long v) {
  Q.push({{x, y}, v});
  for (auto xx : kto) vis[xx.first][xx.second] = 0;
  kto.clear();
  vis[x][y] = 1;
  while (!Q.empty()) {
    int xx = Q.front().first.first, yy = Q.front().first.second;
    long long vv = Q.front().second;
    val[xx][yy] += vv;
    Q.pop();
    kto.push_back({xx, yy});
    vv /= 2;
    if (vv == 0) continue;
    for (int i = 0; i < 8; i += 2) {
      int ux = xx + p[i], uy = yy + p[i + 1];
      if (s[ux][uy] == '*') continue;
      if (1 > ux || ux > n || 1 > uy || uy > m) continue;
      if (!vis[ux][uy]) {
        vis[ux][uy] = 1;
        Q.push({{ux, uy}, vv});
      }
    }
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m >> q >> P;
  for (int i = 1; i <= n; i++) cin >> (s[i] + 1);
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if ('A' <= s[i][j] && s[i][j] <= 'Z') {
        long long vv = (long long)(s[i][j] - 'A' + 1) * q;
        bfs(i, j, vv);
      }
    }
  }
  int ans = 0;
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) {
      if (val[i][j] > P) ans++;
    }
  cout << ans << "\n";
  return 0;
}
