/* Aa^~ kokoro ga pyonpyon suru n jaa^~
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*/
#include<bits/stdc++.h>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x...) do { cout << "\033[32;1m " << #x << " -> "; err(x); } while (0)
void err() { cout << "\033[39;0m" << endl; }
template<template<typename...> class T, typename t, typename... A>
void err(T<t> a, A... x) { for (auto v: a) cout << v << ' '; err(x...); }
template<typename T, typename... A>
void err(T a, A... x) { cout << a << ' '; err(x...); }
#else
#define dbg(...)
#endif
typedef long long ll;
typedef pair<int,int> pi;
typedef vector<int> vi;
template<class T> using vc=vector<T>;
template<class T> using vvc=vc<vc<T>>;
template<class T> void mkuni(vector<T>&v)
{
    sort(v.begin(),v.end());
    v.erase(unique(v.begin(),v.end()),v.end());
}
ll rand_int(ll l, ll r) //[l, r]
{
    static mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count());
    return uniform_int_distribution<ll>(l, r)(gen);
}
template<class T>
void print(T x,int suc=1)
{
    cout<<x;
    if(suc==1) cout<<'\n';
    else cout<<' ';
}
template<class T>
void print(const vector<T>&v,int suc=1)
{
    for(int i=0;i<v.size();i++)
    print(v[i],i==(int)(v.size())-1?suc:2);
}
const int maxn=105;
string maze[maxn];
int vis[maxn][maxn];
int main()
{
    int h,w;
    cin>>h>>w;
    memset(vis,0x3f,sizeof(vis));
    for(int i=0;i<h;i++) cin>>maze[i];
    deque<pi> q;
    vis[0][0]=maze[0][0]=='#';
    q.push_back({0,0});
    while(!q.empty())
    {
        auto u=q.front();q.pop_front();
        int nx=u.first+1,ny=u.second+1;
        if(nx<h)
        {
            int d=0;
            if(maze[u.first][u.second]=='.'&&maze[nx][u.second]=='#') d++;
            if(vis[nx][u.second]>vis[u.first][u.second]+d)
            {
                vis[nx][u.second]=vis[u.first][u.second]+d;
                if(d==0)
                    q.push_front(make_pair(nx,u.second));
                else q.push_back(make_pair(nx,u.second));
            }
        }
        if(ny<w)
        {
            int d=0;
            if(maze[u.first][u.second]=='.'&&maze[u.first][ny]=='#') d++;
            if(vis[u.first][ny]>vis[u.first][u.second]+d)
            {
                vis[u.first][ny]=vis[u.first][u.second]+d;
                if(d==0)
                    q.push_front(make_pair(u.first,ny));
                else q.push_back(make_pair(u.first,ny));
            }
        }
    }
    cout<<vis[h-1][w-1]<<'\n';

}

Measured memory_bytes: 256