import strutils, sequtils, sets

when isMainModule:
  var
    tmp = stdin.readLine.split.map(parseInt)
    (n, m) = (tmp[0], tmp[1])
    a = newSeqWith(m, newSeqWith(n, newSeq[int](n)))

  for i in 0..m-1:
    for j in 0..n-1:
      a[i][j] = stdin.readLine.split.map(parseInt)

  var min = 1 shl 30

  for i in 0..m-1:
    for j in i+1..m-1:
      # yoko * yoko
      for li in 0..n-1:
        for lj in 0..n-1:
          var cnt = initSet[int]()
          for ci in 0..n-1:
            cnt.incl(a[i][li][ci])
          for cj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

      # tate * tate
      for ci in 0..n-1:
        for cj in 0..n-1:
          var cnt = initSet[int]()
          for li in 0..n-1:
            cnt.incl(a[i][li][ci])
          for lj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

      # yoko * tate
      for li in 0..n-1:
        for cj in 0..n-1:
          var cnt = initSet[int]()
          for ci in 0..n-1:
            cnt.incl(a[i][li][ci])
          for lj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

      # tate * yoko
      for ci in 0..n-1:
        for lj in 0..n-1:
          var cnt = initSet[int]()
          for li in 0..n-1:
            cnt.incl(a[i][li][ci])
          for cj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

      # naname * naname
      for si in 0..1:
        for sj in 0..1:
          var cnt = initSet[int]()
          for k in 0..n-1:
            if si == 0: cnt.incl(a[i][k][k])
            else: cnt.incl(a[i][k][n-k-1])
          for k in 0..n-1:
            if sj == 0: cnt.incl(a[j][k][k])
            else: cnt.incl(a[j][k][n-k-1])
          min = min(min, cnt.len)

      # yoko * naname
      for li in 0..n-1:
        for sj in 0..1:
          var cnt = initSet[int]()
          for ci in 0..n-1:
            cnt.incl(a[i][li][ci])
          for k in 0..n-1:
            if sj == 0: cnt.incl(a[j][k][k])
            else: cnt.incl(a[j][k][n-k-1])
          min = min(min, cnt.len)

      # naname * yoko
      for si in 0..1:
        for lj in 0..n-1:
          var cnt = initSet[int]()
          for k in 0..n-1:
            if si == 0: cnt.incl(a[i][k][k])
            else: cnt.incl(a[i][k][n-k-1])
          for cj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

      # tate * naname
      for ci in 0..n-1:
        for sj in 0..1:
          var cnt = initSet[int]()
          for li in 0..n-1:
            cnt.incl(a[i][li][ci])
          for k in 0..n-1:
            if sj == 0: cnt.incl(a[j][k][k])
            else: cnt.incl(a[j][k][n-k-1])
          min = min(min, cnt.len)

      # naname * tate
      for si in 0..1:
        for cj in 0..n-1:
          var cnt = initSet[int]()
          for k in 0..n-1:
            if si == 0: cnt.incl(a[i][k][k])
            else: cnt.incl(a[i][k][n-k-1])
          for lj in 0..n-1:
            cnt.incl(a[j][lj][cj])
          min = min(min, cnt.len)

  echo min - 1