package chelper;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Set;

import io.InputReader;
import io.OutputWriter;
import misc.SimpleSavingChelperSolution;


public class I extends SimpleSavingChelperSolution {

  public void solve(int testNumber, InputReader in, OutputWriter out) {
    wrapSolve(testNumber, in, out);
  }

  int[][] dirs = {
      {0, 1},
      {0, -1},
      {1, 0},
      {-1, 0},
  };

  @Override
  public void solve(int testNumber) {
    int n = in.nextInt();
    int m = in.nextInt();

    long q = in.nextLong();
    long p = in.nextLong();

    long[][] starts = new long[n][m];

    boolean[][] walls = new boolean[n][m];

    for (int i = 0; i < n; i++) {
      String s = in.nextString();

      for (int j = 0; j < m; j++) {
        char c = s.charAt(j);

        walls[i][j] = c == '*';

        long k = c - 'A' + 1;

        if (k >= 1 && k <= 26) {
          starts[i][j] = k * q;
        }
      }
    }

    long[][] res = new long[n][m];

    int[][] Q = new int[10000][2];

    boolean[][] visited = new boolean[n][m];

    for (int sx = 0; sx < n; sx++) {
      for (int sy = 0; sy < m; sy++) {
//        sx = 100;
//        sy = 100;

        if (starts[sx][sy] == 0) {
          continue;
        }

        int qs = 0;
        int ql = 0;

        long v = starts[sx][sy];
//        long vt = ((long) sx) * m + sy;

        visited[sx][sy] = true;
        Q[ql][0] = sx;
        Q[ql++][1] = sy;

        res[sx][sy] += v;
        int waveSize = 1;

        v /= 2;

        while (waveSize != 0 && v > 0) {
          int nextWaveSize = 0;
//          out.println(waveSize + " " + ql + " " + v);

          for (int i = 0; i < waveSize; i++) {
            int x = Q[qs + i][0];
            int y = Q[qs + i][1];

            for (int ii = 0; ii < 4; ii++) {
              int xx = x + dirs[ii][0];
              int yy = y + dirs[ii][1];

              if (xx < 0 || yy < 0 || xx >= n || yy >= m || visited[xx][yy] || walls[xx][yy]) {
                continue;
              }

              res[xx][yy] += v;

              visited[xx][yy] = true;
              Q[ql][0] = xx;
              Q[ql++][1] = yy;

              nextWaveSize++;
            }
          }
          qs += waveSize;

          waveSize = nextWaveSize;
          v /= 2;
        }

        for (int i = 0; i < ql; i++) {
          visited[Q[i][0]][Q[i][1]] = false;
        }

//        return;

      }
    }


//    for (int letter = 0; letter < 26; letter++) {
//      if (starts[letter][0] == -1) {
//        continue;
//      }
//
//      long v = (letter + 1) * q;
//
//      List<int[]> next = new ArrayList<>();
//      next.add(starts[letter]);
//
//      boolean[][] visited = new boolean[n][m];
//
//      while (!next.isEmpty()) {
//        List<int[]> nnext = new ArrayList<>();
//        for (int[] ints : next) {
//          int x = ints[0];
//          int y = ints[1];
//
//          visited[x][y] = true;
//          res[x][y] += v;
//
//          for (int[] dir : dirs) {
//            int xx = x + dir[0];
//            int yy = y + dir[1];
//
//            if (xx < 0 || yy < 0 || xx >= n || yy >= m || visited[xx][yy]) {
//              continue;
//            }
//
//            nnext.add(new int[]{xx, yy});
//          }
//        }
//
//        next = nnext;
//        v /= 2;
//      }

//    for (int i = 0; i < n; i++) {
//      for (int j = 0; j < m; j++) {
//        out.print(res[i][j] + " ");
//      }
//      out.println();
//    }

    int ans = 0;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < m; j++) {
        if (res[i][j] > p) {
          ans++;
        }
      }
    }

    out.println(ans);
  }
}