字母矩阵

import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] params = br.readLine().split(" ");
        int n = Integer.parseInt(params[0]);
        int m = Integer.parseInt(params[1]);
        int k = Integer.parseInt(params[2]);
        char[][] matrix = new char[n][];
        for(int i = 0; i < n; i++){
            matrix[i] = br.readLine().toCharArray();
        }
        int resEdge = -1;
        for(int edge = Math.min(n, m); edge >= (int)Math.ceil(Math.sqrt(k)); edge--){
            if(convolution(matrix, edge, k)){
                resEdge = edge;
            }else{
                break;
            }
        }
        System.out.println(resEdge);
    }
    
    private static boolean convolution(char[][] matrix, int edge, int lb){
        // 从左上角初始化计数器
        int[] counter = new int[26];
        int nunique = 0;
        for(int i = 0; i < edge; i++){
            for(int j = 0; j < edge; j++){
                if(counter[matrix[i][j] - 'a'] == 0){
                    nunique++;
                }
                counter[matrix[i][j] - 'a']++;
            }
        }
        if(nunique >= lb){
            return true;
        }
        // 之字形滑动窗口
        boolean left2right = true;     // 先从左往右滑动
        for(int i = 0; i <= matrix.length - edge; i++){
            if(left2right){
                for(int j = 0; j <= matrix[0].length - edge; j++){
                    if(j > 0){
                        for(int r = i; r < i + edge; r++){
                            counter[matrix[r][j - 1] - 'a']--;
                            if(counter[matrix[r][j - 1] - 'a'] == 0){
                                nunique--;
                            }
                            counter[matrix[r][j + edge - 1] - 'a']++;
                            if(counter[matrix[r][j + edge - 1] - 'a'] == 1){
                                nunique++;
                            }
                        }
                    }
                    if(nunique >= lb){
                        return true;
                    }
                }
                // 构建下一行的初始窗口
                if(i + edge < matrix.length){
                    for(int k = matrix[0].length - edge; k < matrix[0].length; k++){
                        counter[matrix[i][k] - 'a']--;
                        if(counter[matrix[i][k] - 'a'] == 0){
                            nunique--;
                        }
                        counter[matrix[i + edge][k] - 'a']++;
                        if(counter[matrix[i + edge][k] - 'a'] == 1){
                            nunique++;
                        }
                    }
                }
            }else{
                for(int j = matrix[0].length - edge; j >= 0; j--){
                    if(j < matrix[0].length - edge){
                        for(int k = i; k < i + edge; k++){
                            counter[matrix[k][j + edge] - 'a']--;
                            if(counter[matrix[k][j + edge] - 'a'] == 0){
                                nunique--;
                            }
                            counter[matrix[k][j] - 'a']++;
                            if(counter[matrix[k][j] - 'a'] == 1){
                                nunique++;
                            }
                        }
                    }
                    if(nunique >= lb){
                        return true;
                    }
                }
                if(i + edge < matrix.length){
                    for(int k = 0; k < edge; k++){
                        counter[matrix[i][k] - 'a']--;
                        if(counter[matrix[i][k] - 'a'] == 0){
                            nunique--;
                        }
                        counter[matrix[i + edge][k] - 'a']++;
                        if(counter[matrix[i + edge][k] - 'a'] == 1){
                            nunique++;
                        }
                    }
                }
            }
            left2right = !left2right;
        }
        return false;
    }
}