#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;
using namespace std;


#define fast ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define PSET(x,y) fixed<<setprecision(y)<<x
#define pb push_back
#define pii pair<int,int>
#define pf push_front
#define mp make_pair
#define vi vector<int>
#define vip vector<pair<int,int> >
#define ff first
#define ss second
#define int long long
#define mod 1000000007
#define BIG 998244353
#define s(t) scanf("%lld",&t)
#define p(t) printf("%lld\n",t)
#define mii map<int,int>
#define MSET(table,i) memset(table, i, sizeof(table))
#define endl '\n'
#define tc int t;cin>>t;while(t--)
#define pi  3.1415926358
#define bits(x) __builtin_popcount(x)
#define minimum(a,n) min_element(a,a+n)-a
#define maximum(a,n) max_element(a,a+n)-a
#define pqbig priority_queue<int>
#define pqsmall priority_queue<pair<int,pii>,vector<pair<int,pii> >,greater<pair<int,pii> > >
#define all(v) v.begin(),v.end()
#define sitr set<int>:: iterator
#define spitr set<pii>:: iterator
#define mitr map<string,int>:: iterator

int toint(const string &s) {stringstream ss; ss << s; int x; ss >> x; return x;}
string tostring ( int number ) {stringstream ss; ss << number; return ss.str();}

typedef tree<pii, null_type, less<pii>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

#define trace1(x)                cerr<<#x<<": "<<x<<endl
#define trace2(x, y)             cerr<<#x<<": "<<x<<" | "<<#y<<": "<<y<<endl
#define trace3(x, y, z)          cerr<<#x<<":" <<x<<" | "<<#y<<": "<<y<<" | "<<#z<<": "<<z<<endl
#define trace4(a, b, c, d)       cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<endl
#define trace5(a, b, c, d, e)    cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<endl
#define trace6(a, b, c, d, e, f) cerr<<#a<<": "<<a<<" | "<<#b<<": "<<b<<" | "<<#c<<": "<<c<<" | "<<#d<<": "<<d<<" | "<<#e<< ": "<<e<<" | "<<#f<<": "<<f<<endl

const int N=105;
int dp[N][N];
char arr[N][N];
int n,m;

int32_t main()
{
    fast;
    cin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
            cin>>arr[i][j];
    }

    if(arr[1][1]=='#')
        dp[1][1]=1;

    for(int i=2;i<=m;i++)
    {
        if(arr[1][i-1]=='#' or arr[1][i]=='.')
            dp[1][i]=dp[1][i-1];
        else
                dp[1][i]=dp[1][i-1]+1;
    }

    for(int i=2;i<=n;i++)
    {
        if(arr[i-1][1]=='#' or arr[i][1]=='.')
            dp[i][1]=dp[i-1][1];
        else
            dp[i][1]=dp[i-1][1]+1;
    }

    for(int i=2;i<=n;i++)
    {
        for(int j=2;j<=m;j++)
        {
            if(arr[i][j]=='.')
                dp[i][j]=min(dp[i-1][j],dp[i][j-1]);
            else
            {
                int val1,val2;
                if(arr[i-1][j]=='#')
                    val1=dp[i-1][j];
                else
                    val1=dp[i-1][j]+1;
                if(arr[i][j-1]=='#')
                    val2=dp[i][j-1];
                else
                    val2=dp[i][j-1]+1;

                dp[i][j]=min(val1,val2);
            }
        }
    }
    cout<<dp[n][m];
}

Measured memory_bytes: 384