#include <bits/stdc++.h>
using namespace std;
const int maxn = 7e5 + 10;
const int inf = 0x3f3f3f3f;
int n, m, p, q, nx, ny;
long long sum[300][300];
int dis[300][300];
int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};
char maze[300][300];
bool check(int x, int y) {
  if (x >= 1 && x <= n && y >= 1 && y <= m && maze[nx][ny] != '*') {
    return true;
  }
  return false;
}
void bfs(int sx, int sy, long long k) {
  dis[sx][sy] = 0, sum[sx][sy] += k;
  queue<pair<pair<int, int>, int> > q;
  q.push(make_pair(make_pair(sx, sy), k));
  while (q.empty() == 0) {
    pair<pair<int, int>, int> tmp = q.front();
    q.pop();
    for (int i = 0; i < 4; i++) {
      nx = tmp.first.first + dx[i], ny = tmp.first.second + dy[i];
      if (check(nx, ny) && dis[nx][ny] == inf) {
        dis[nx][ny] = dis[tmp.first.first][tmp.first.second] + 1;
        int res = tmp.second / 2;
        if (res <= 0) {
          break;
        }
        sum[nx][ny] += res;
        q.push(make_pair(make_pair(nx, ny), res));
      }
    }
  }
}
int main() {
  cin >> n >> m >> q >> p;
  memset(sum, 0, sizeof(sum));
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    cin >> maze[i] + 1;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (maze[i][j] >= 'A' && maze[i][j] <= 'Z') {
        memset(dis, inf, sizeof(dis));
        bfs(i, j, (maze[i][j] - 'A' + 1) * q);
      }
    }
  }
  int ans = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (sum[i][j] > p && maze[i][j] != '*') {
        ans++;
      }
    }
  }
  cout << ans << endl;
  return 0;
}
