#include <bits/stdc++.h>
using namespace std;
#define BIT(n) (1LL << (n))
#define BITF(n, i) (((n) >> (i)) & 1)
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define REPI(i, x) for (int i = 1; i <= x; i++)
#define FORI(i, m, n) for (int i = m; i <= n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define REPZ(i, x) for (int i = 0; i <= x; i++)
#define FORA(i, n) for (auto &&i : n)
#define POW(a, b) ((int)(pow(a, b) + .5))
#define MODULO(a, b) (((a) % (b)) < 0 ? (a) % (b) + (b) : (a) % (b))
#define DUMPOUT cerr
// vector
template <typename T> istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec) is >> x;
  return is;
}
// pair
template <typename T, typename U> ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}
// vector
template <typename T> ostream &operator<<(ostream &os, const vector<T> &vec) {
  os << "{";
  REP(i, (int)vec.size())
  os << vec[i] << (i + 1 == (int)vec.size() ? "" : ", ");
  os << "}";
  return os;
}
// map
template <typename T, typename U> ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "{";
  FORA(itr, map_var) {
    os << *itr;
    itr++;
    if (itr != map_var.end()) os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
// set
template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "{";
  FORA(itr, set_var) {
    os << *itr;
    itr++;
    if (itr != set_var.end()) os << ", ";
    itr--;
  }
  os << "}";
  return os;
}
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head &&head, Tail &&... tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) > 0) DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}
#ifdef DEBUG_
#define DEB
#define DUMP(...)                                                             \
  DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                             \
          << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl \
          << "    ",                                                          \
      dump_func(__VA_ARGS__)
#define PRINTARR(x, y)                                     \
  cerr << #x << "=\n";                                     \
  for (auto itr = x; itr != y; itr++) cerr << *itr << " "; \
  cerr << endl;
#define PRINTARR2(x, i0, i1)                                       \
  cerr << #x << "=\n";                                             \
  for (int ii0 = 0; ii0 < i0; ii0++) {                             \
    for (int ii1 = 0; ii1 < i1; ii1++) cerr << x[ii0][ii1] << " "; \
    cerr << endl;                                                  \
  }
#else
#define DEB if (false)
#define DUMP(...)
#define PRINTARR(x, y)
#define PRINTARR2(x, i0, i1)
#endif
#define ALL(v) v.begin(), v.end()
#define fst first
#define snd second
#define mp make_pair
#define pb push_back
#define epb emplace_back
#define int long long
#define pint pair<int, int>
#define pdouble pair<double, double>
#define ld long double
using namespace std;
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> using vec = std::vector<T>;
template <class T> void print(const T &x) { cout << x << "\n"; }
const int MOD = 1000000007, INF0 = 1061109567, INF = INF0 * INF0;
const double EPS = 1e-7, PI = acos(-1.0);
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
/*  set UnionFind BIT deque queue multiset segtree priority_queue bitset map vector
[&] { return; }();下のスラッシュを2つ追加しただけ.上のスラッシュを2つにすれば外れる.
//*/
#define MAXN 110
#define MAXN2 (2 * MAXN * MAXN)
struct edge {
  int to, cost;
};
vec<edge> G[(MAXN2)];
int d[MAXN2];
void dijkstra(int s) {
  priority_queue<pint, vec<pint>, greater<pint>> que;
  fill(d, d + MAXN2, INF);
  d[s] = 0;
  que.push(pint(d[s], s));
  while (!que.empty()) {
    pint p = que.top();
    que.pop();
    int v = p.snd;
    if (d[v] < p.fst) {
      continue;  // chmin関数でd[e.to]が複数回更新される可能性？
                 // ここで呼び出される前に最短が更新されているのかもしれない。
    }
    FORA(e, G[v]) {
      bool p = chmin(d[e.to], d[v] + e.cost);
      if (p) {
        que.push(pint(d[e.to], e.to));  //
      }
    }
  }
}

char s[MAXN][MAXN];
int dp[MAXN][MAXN];
map<int, vec<int>> ma;
signed main() {
  cin.tie(0), ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  int H, W;
  cin >> H >> W;
  REP(i, H) {
    REP(j, W) { cin >> s[i][j]; }
  }
  int addcost = (s[0][0] == '#') + (s[H - 1][W - 1] == '#');
  //  s[0][0] = '.';
  // s[H - 1][W - 1] = '.';
  fill((int *)dp, (int *)dp[MAXN], INF);
  dp[0][0] = 0;
  REP(i, H) {
    REP(j, W) {
      if (i + 1 < H) chmin(dp[i + 1][j], dp[i][j] + (s[i + 1][j] != s[i][j]));
      if (j + 1 < W) chmin(dp[i][j + 1], dp[i][j] + (s[i][j + 1] != s[i][j]));
    }
  }

  /*REP(i, H) {
    REP(j, W - 1) {
      int index = i * (W - 1) + j;
      int tmp = i * W + j;
      ma[tmp].pb(index);
      ma[tmp + 1].pb(index);
      DUMP(index, index + 1, index);
    }
  }
  int add = H * (W - 1);
  REP(j, W) {
    REP(i, H - 1) {
      int index = j + i * W;
      int p = j * (H - 1) + i + add;
      ma[index].pb(p);
      ma[index + W].pb(p);
      DUMP(index, index + W, p);
    }
  }
  REP(i, H) {
    REP(j, W) {
      int index = i * W + j;
      int cost = s[i][j] == '#';
      if (index == 0 || index == H * W - 1) continue;
      FORA(e, ma[index]) {
        FORA(e2, ma[index]) {
          if (e != e2) {
            DUMP(e, e2, index);
            G[e].pb(edge{e2, cost});
          }
        }
      }
    }
  }
  REP(i, H * (W - 1) + W * (H - 1)) {
    FORA(e, G[i]) { DUMP(i, e.to, e.cost); }
  }
  int ans = INF;
  int arr[4] = {0, H * (W - 1), H * (W - 1) - 1, H * (W - 1) + W * (H - 1) - 1};
  REP(i, 2) {
    dijkstra(arr[i]);
    DUMP(d[arr[2]], d[arr[3]]);
    chmin(ans, d[arr[2]]);
    chmin(ans, d[arr[3]]);
  }
  DUMP(addcost);*/
  print((dp[H - 1][W - 1] + addcost) / 2);
}

Measured memory_bytes: 896