#include <vector>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <numeric>
#include <sstream>
#include <iostream>
#include <iomanip>
#define _USE_MATH_DEFINES
#include <cmath>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cfloat>
#include <cmath>
#include <ctime>
#include <cassert>
#include <cctype>
#include <cstdio>
#include <cassert>
using namespace std;

#define EPS 1e-12
#define ull unsigned long long
#define ll long long
#define VI vector<ll>
#define PII pair<ll, ll> 
#define VVI vector<vector<ll> >
#define VVVI vector<vector<vector<ll>>>
#define VVVVI vector<vector<vector<vector<ll>>>>
#define REP(i,n) for(ll i=0,_n=(n);(i)<(ll)_n;++i)
#define REPR(i,n) for(ll i=(ll)(n)-1;0<=(i);--i)
#define RANGE(i,a,b) for(ll i=(ll)a,_b=(ll)(b);(i)<_b;++i)
#define RANGER(i,a,b) for(ll i=(ll)(b)-1,_a=(ll)(a);(_a)<=i;--i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
#define ALLR(c) (c).rbegin(), (c).rend()
#define PB push_back
#define MP(a, b) make_pair(a, b)
#define POPCOUNT __builtin_popcount
#define POPCOUNTLL __builtin_popcountll
#define CLEAR(table, v) memset(table, v, sizeof(table));
#define UNIFORM_DOUBLE(a, b) (((b-a)*(double)rand()/RAND_MAX)+a) // [a, b) 
#define UNIFORM_LL(a, b) (ll)UNIFORM_DOUBLE(a, b) // [a, b) 
#define IN(v, lo, hi) ((lo)<=(v) && (v)<(hi))
#define DD(v) cout<<#v<<": "<<v<<endl
#define FI first
#define SE second
template <typename T0, typename T1> std::ostream& operator<<(std::ostream& os, const map<T0, T1>& v) { for( typename map<T0, T1>::const_iterator p = v.begin(); p!=v.end(); p++ ){os << p->first << ": " << p->second << " ";} return os; }
template <typename T0, typename T1> std::ostream& operator<<(std::ostream& os, const pair<T0, T1>& v) { os << v.first << ": " << v.second << " "; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const vector<T>& v) { for( int i = 0; i < (int)v.size(); i++ ) { os << v[i] << " "; } return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const set<T>& v) { vector<T> tmp(v.begin(), v.end()); os << tmp; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const deque<T>& v) { vector<T> tmp(v.begin(), v.end()); os << tmp; return os; }
template <typename T> std::ostream& operator<<(std::ostream& os, const vector<vector<T> >& v) { for( int i = 0; i < (int)v.size(); i++ ) { os << v[i] << endl; } return os; }
template<typename T>void maxUpdate(T& a, T b) {a = max(a, b);}
template<typename T>void minUpdate(T& a, T b) {a = min(a, b);}

#define INF (1LL<<60)

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	ll W,H;
	while(cin>>H>>W) {
		vector<string> m(H);
		REP(i, H) cin>>m[i];
		// [i][y][x]: i: (x, y) を反転したかどうか
		VVVI dp(2, VVI(H, VI(W, INF)));
		REP(y, H) REP(x, W) REP(ii, 2) {
			ll v=INF;
			if(!(0<=y-1) && !(0<=x-1)) {
				if(ii==0 && m[y][x]=='.') v = 0;
				if(ii==1 && m[y][x]=='#') v = 1;
			}
			if(0<=y-1) {
				if(ii==0 && m[y][x]=='.') minUpdate(v, min(dp[0][y-1][x], dp[1][y-1][x]));
				if(ii==1 && m[y][x]=='#') minUpdate(v, min(dp[0][y-1][x]+1, dp[1][y-1][x]));
			}
			if(0<=x-1) {
				if(ii==0 && m[y][x]=='.') minUpdate(v, min(dp[0][y][x-1], dp[1][y][x-1]));
				if(ii==1 && m[y][x]=='#') minUpdate(v, min(dp[0][y][x-1]+1, dp[1][y][x-1]));
			}
			dp[ii][y][x] = v;
		}
//		DD(dp);
		ll ans = min(dp[0][H-1][W-1], dp[1][H-1][W-1]);
		cout<<ans<<endl;
	}
	
	return 0;
}


Measured memory_bytes: 512