#include <bits/stdc++.h>
using namespace std;
const int MX = 255;
int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};
char s[MX][MX];
long long tot[MX][MX];
int was[MX][MX];
int cur[MX][MX];
int main() {
  int n, m, p, w;
  scanf("%d %d %d %d", &n, &m, &p, &w);
  for (int i = 1; i <= n; i++) {
    scanf("%s", s[i]);
    for (int j = m; j >= 1; j--) {
      s[i][j] = s[i][j - 1];
    }
    s[i][0] = '\0';
  }
  int cnt = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (s[i][j] >= 'A' && s[i][j] <= 'Z') {
        cnt++;
        queue<pair<int, int> > q;
        q.push(make_pair(i, j));
        cur[i][j] = p * (s[i][j] - 'A' + 1);
        was[i][j] = cnt;
        while (!q.empty()) {
          int xx = q.front().first, yy = q.front().second;
          q.pop();
          tot[xx][yy] += cur[xx][yy];
          for (int dir = 0; dir < 4; dir++) {
            int nx = xx + dx[dir], ny = yy + dy[dir];
            if (was[nx][ny] != cnt && cur[xx][yy] / 2 > 0 && s[nx][ny] != '*' &&
                nx >= 1 && nx <= n && ny >= 1 && ny <= m) {
              was[nx][ny] = cnt;
              cur[nx][ny] = cur[xx][yy] / 2;
              q.push(make_pair(nx, ny));
            }
          }
        }
      }
    }
  }
  int res = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (tot[i][j] > w) res++;
    }
  }
  printf("%d\n", res);
}
