#!/usr/bin/python3
# checks to see if all the labeled regions are connected

import sys

class node:
  def __init__(self,id):
    self.label = 0
    self.nbr = []
    self.visited = False

# count cells in a connected component, see if that matches the count
# recorded for that block
def compcount(v,c):
  count = dfs(v)
  if count != c:
    print(f'Block {graph[v].label} not connected')
    sys.exit(43)

# depth first search a connected region
def dfs(v):
  count = 1
  graph[v].visited = True
  for i in graph[v].nbr:
    if graph[i].visited: continue
    count += dfs(i)
  return count

# input everything
(rows,cols) = map(int,sys.stdin.readline().split())
grid=[]
for i in range(rows):
  grid.append(list(map(int,sys.stdin.readline().split())))

# maps each region to a cell count and a starting cell:
d = {}

# build a graph; edges between cells that have the same label:
graph = [node(i) for i in range(rows*cols)]

for r in range(rows):
  for c in range(cols):
    g1 = r*cols+c
    graph[g1].label = grid[r][c]
    if r-1 >= 0 and grid[r][c] == grid[r-1][c]:
      g2 = (r-1)*cols+c
      graph[g1].nbr.append(g2)
      graph[g2].nbr.append(g1)

    if c-1 >= 0 and grid[r][c] == grid[r][c-1]:
      g2 = r*cols+c-1
      graph[g1].nbr.append(g2)
      graph[g2].nbr.append(g1)

    # have we seen this label before?
    cell = d.get(grid[r][c],None)
    if cell == None: # new label; save cell location and set count = 1
      d[grid[r][c]] = [r,c,1]
    else: # already seen this label; just update the count
      cell[2] += 1

# Now check each labeled region to make sure it's connected:
for k in d:
  [r,c,count] = d[k]
  compcount(r*cols+c,count)
sys.exit(42)