[백준] 1051

n, m = map(int, input().split())

arr = [[0 for i in range(m)] for i in range(n)]
for i in range(n):
  s = input()
  for j in range(m):
    arr[i][j] = int(s[j])

if n==1 or m==1:
  print(1)
else:
  cnt = 0
  for r in range(min([n, m]), 1, -1):
    r -= 1
    if cnt == 1: break;
    for i in range(0, m-r):
      if  cnt == 1: break;
      for j in range(0, n-r):
        if arr[j][i] == arr[j+r][i] == arr[j][i+r] == arr[j+r][i+r]:
          print((r+1)**2); cnt = 1; break;
  if cnt == 0:
    print(1)