package main
import (
  "bufio"
  "os"
  "strconv"
  "strings"
  "fmt"
  "container/heap"
)

var reader = bufio.NewReaderSize(os.Stdin, 1000000)
var writer = bufio.NewWriter(os.Stdout)
func NextLine() string {
  buffer := make([]byte, 0)
  for true {
    line, isPrefix, err := reader.ReadLine()
    if err != nil { panic(err) }
    buffer = append(buffer, line...)
    if !isPrefix { break }
  }
  return string(buffer)
}
func NextInt(A ...*int) {
  L := strings.Split(NextLine(), " ")
  for i, a := range A {
    *a, _ = strconv.Atoi(L[i])
  }
}
func NextIntVec(A *[]int) {
  L := strings.Split(NextLine(), " ")
  (*A) = make([]int, len(L))
  for i, l := range L {
    (*A)[i], _ = strconv.Atoi(l)
  }
}
func NextFloat(A ...*float64) {
  L := strings.Split(NextLine(), " ")
  for i, a := range A {
    *a, _ = strconv.ParseFloat(L[i], 64)
  }
}
func NextFloatVec(A *[]float64) {
  L := strings.Split(NextLine(), " ")
  (*A) = make([]float64, len(L))
  for i, l := range L {
    (*A)[i], _ = strconv.ParseFloat(l, 64)
  }
}
func Write(s interface{}) {
  fmt.Fprintln(writer, s)
}
func WriteIntVec(A []int) {
  S := make([]string, len(A))
  for i, a := range A {
    S[i] = strconv.Itoa(a)
  }
  Write(strings.Join(S, " "))
}
func Output() {
  _ = writer.Flush()
}

func MaxInt(A ...int) int {
  max := A[0]
  for _, a := range A {
    if max < a { max = a }
  }
  return max
}
func MinInt(A ...int) int {
  min := A[0]
  for _, a := range A {
    if a < min { min = a }
  }
  return min
}
func SumInt(A ...int) int {
  sum := 0
  for _, a := range A {
    sum += a
  }
  return sum
}

type Item struct {
  Priority int
  Entry interface{}
}
type Heap []*Item
func (H Heap) Len() int { return len(H) }
func (H Heap) Less(i, j int) bool { return H[i].Priority < H[j].Priority }
func (H Heap) Swap(i, j int) { H[i], H[j] = H[j], H[i] }
func (H *Heap) Pop() interface{} {
  Old := *H
  n := len(Old)
  item := Old[n - 1]
  *H = Old[0:n - 1]
  return item
}
func (H *Heap) Push(x interface{}) {
  item := x.(*Item)
  *H = append(*H, item)
}
type PriorityQueue struct {
  Comparator func(e interface{}) int
  Items Heap
}
func (PQ *PriorityQueue) Push(e interface{}) {
  item := Item{PQ.Comparator(e), e}
  heap.Push(&PQ.Items, &item)
}
func (PQ *PriorityQueue) Pop() interface{} {
  return heap.Pop(&PQ.Items).(*Item).Entry
}
func InitPQ(F func(interface{}) int) PriorityQueue {
  var H Heap
  return PriorityQueue{F, H}
}

func Solve() {
  var H, W int
  NextInt(&H, &W)
  M := make([][]int, H)
  for i := range M {
    M[i] = make([]int, W)
    for j, s := range NextLine() {
      if s == '#' { M[i][j] = 1 }
    }
  }
  G := make([][][]int, H * W)
  for i := range G {
    G[i] = make([][]int, 0)
  }
  for h := 0; h < H; h++ {
    for w := 0; w < W; w++ {
      x := h * W + w
      if w < W - 1 {
        c := 0
        if M[h][w] != M[h][w + 1] { c++ }
        G[x] = append(G[x], []int{x + 1, c})
      }
      if h < H - 1 {
        c := 0
        if M[h][w] != M[h + 1][w] { c++ }
        G[x] = append(G[x], []int{x + W, c})
      }
    }
  }
  F := func (e interface{}) int { return e.([]int)[0] }
  PQ := InitPQ(F)
  D := make([]int, H * W)
  for i := range D { D[i] = H * W}
  PQ.Push([]int{M[0][0], 0})
  for 0 < PQ.Items.Len() {
    pq := PQ.Pop().([]int)
    c, v := pq[0], pq[1]
    if D[v] <= c { continue }
    D[v] = c
    for _, Adj := range G[v] {
      adj, d := Adj[0], Adj[1]
      if D[adj] <= c + d { continue }
      PQ.Push([]int{c + d, adj})
    }
  }
  Write((D[H * W - 1] + 1) / 2)
}

func main() {
  Solve()
  Output()
}

Measured memory_bytes: 3712