from sys import stdin
 
input = stdin.readline
"""
왜 시간 초과지 ? -> 어떤 부분을 고쳐야 더 빨라질까 ?
"""
 
dys, dxs = [-1, 1, 0, 0], [0, 0, -1, 1]
 
def dfs(y, x, move_cnt):
    print(y, x, move_cnt)
    # print("***********************")
    # print(f"y = {y} / x = {x}")
    # for c_y in range(r):
    #     for c_x in range(c):
    #         print(visited[c_y][c_x], end=" ")
    #     print()
    # print("***********************")
    z = zip(dys, dxs)
    ret = move_cnt
    for dy, dx in z:
        new_y, new_x = y + dy, x + dx
        # 범위를 넘지 않고, 지난 적이 없는 알파벳이라면 -> dfs() 탐색
        if 0 <= new_y < r and 0 <= new_x < c:
            k=alpha_map[new_y][new_x]
            if not alpha_set[k]:
                continue
            alpha_set[k] = False
            ret = max(r, dfs(new_y, new_x, move_cnt+1))
            # 역순으로 돌려놓는 과정
            alpha_set[k] = True  # 미방문 처리
    return ret
 
 
## 변수 입력 부분 ##
r, c = map(int, input().split())  # 1 <= r(행), c(열) <= 20
alpha_map = [[ord(x)-65 for x in input().strip()] for _ in range(r)]  # 알파벳 보드 정보
alpha_set = [True] * 26  # 지나온 알파벳 목록
 
## 문제 해결 부분 ##
alpha_set[alpha_map[0][0]] = False
print(dfs(0, 0, 1))
 

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