#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")

// hloya template v26

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#include <bits/stdc++.h>
using namespace std;

bool dbg = 0;
  
clock_t start_time = clock();
#define current_time fixed<<setprecision(6)<<(ld)(clock()-start_time)/CLOCKS_PER_SEC
  
#define f first
#define s second
#define mp make_pair
// #define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(v) (v).begin(), (v).end()
#define sz(v) ((int)(v).size())
#define sqr(x) ((x) * (x))


#define ull unsigned long long
#define ll long long
#define ld long double
#define pii pair<int,int>
#define umap unordered_map<int, int>
  
#define files1 freopen("input.txt","r",stdin)
#define files2 freopen("output.txt","w",stdout)
#define files files1;files2
#define fast_io ios_base::sync_with_stdio(0);cin.tie(0)
  
// #define endl '\n'
#define ln(i,n) " \n"[(i) == (n) - 1]
  
void bad(string mes = "Impossible"){cout << mes;exit(0);}
void bad(int mes){cout << mes;exit(0);}
  
template<typename T>
string bin(T x, int st = 2){
    string ans = "";
    while (x > 0){
        ans += char('0' + x % st);
        x /= st;
    }
    reverse(ans.begin(), ans.end());
    return ans.empty() ? "0" : ans;
}
  
mt19937_64 mt_rand(
    chrono::system_clock::now().time_since_epoch().count()
);

template<typename T1, typename T2> inline bool upmax(T1& a, T2 b) { return (a < b ? (a = b, true) : false); }
template<typename T1, typename T2> inline bool upmin(T1& a, T2 b) { return (b < a ? (a = b, true) : false); }

// inline int popcount(int x){
//     int count = 0;
//     __asm__ volatile("POPCNT %1, %0;":"=r"(count):"r"(x):);
//     return count;
// }
  
template<typename T>
T input(){
    T ans = 0, m = 1;
    char c = ' ';
  
    while (!((c >= '0' && c <= '9') || c == '-')) {
        c = getchar();
    }
  
    if (c == '-')
        m = -1, c = getchar();
    while (c >= '0' && c <= '9'){
        ans = ans * 10 + (c - '0'), c = getchar();
    }
    return ans * m;
}

template<typename T>
T gcd (T a, T b) { while (b) { a %= b; swap (a, b); } return a; }
  
template<typename T> void read(T& a) { a = input<T>(); }
template<typename T> void read(T& a, T& b) { read(a), read(b); }
template<typename T> void read(T& a, T& b, T& c) { read(a, b), read(c); }
template<typename T> void read(T& a, T& b, T& c, T& d) { read(a, b), read(c, d); }
  
const int inf = 1e9 + 20;
const short short_inf = 3e4 + 20;
const long double eps = 1e-12;
const int maxn = (int)4e6 + 450, base = 998244353;
const ll llinf = 4e18 + 5;
const int mod = 1e9 + 7;

int dp[105][105][2];
int a[105][105];

int main() {
    // files1;
    fast_io;

    int n, m;
    cin >> n >> m;

    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) {
            char c; cin >> c;
            a[i][j] = c == '#';
        }

    for (int i = 0; i < 105; i++)
        for (int j = 0; j < 105; j++)
            dp[i][j][0] = dp[i][j][1] = inf;
    
    dp[0][0][a[0][0]] = a[0][0];
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
            for (int k = 0; k < 2; k++) {
                for (int newk = 0; newk < 2; newk++) {
                    if (i + 1 < n && (newk ^ a[i + 1][j]) == 0) {
                        int val = (k == 0 && newk == 1);
                        upmin(dp[i + 1][j][newk], dp[i][j][k] + val);
                    }
                    if (j + 1 < m && (newk ^ a[i][j + 1]) == 0) {
                        int val = (k == 0 && newk == 1);
                        upmin(dp[i][j + 1][newk], dp[i][j][k] + val);
                    }
                }
            }

    cout << min(dp[n - 1][m - 1][0], dp[n - 1][m - 1][1]);
    return 0;
}

Measured memory_bytes: 384