// #pragma GCC optimize("O3")
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define N 1000000007
#define N2 998244353
#define Nmax 300005
#define INF (ll)1e18
#define pll pair<ll,ll>
#define mp make_pair
#define fi first
#define se second
#define vv vector
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(ll i=m;i<(n);i++)
#define repr(i,n) repr2(i,n,0)
#define repr2(i,m,n) for(ll i=m;i>=(n);i--)
#define get(n) ll (n); scanf("%lld",&(n));
#define get2(n,k) ll (n),(k); scanf("%lld%lld",&(n),&(k));
#define get3(n,m,k) ll (n),(m),(k); scanf("%lld%lld%lld",&(n),&(m),&(k));
#define gets(s) string (s); cin >> (s);
#define ALL(c) (c).begin(),(c).end()
#define fill_nums(A,n) vector<ll> A((n)); for(ll i=0;i<n;i++) scanf("%lld",&A[i]);
#define fill_edges(adj,m) for(ll i=0;i<m;i++) {ll a, b; scanf("%lld %lld",&a,&b); adj[a-1].pb(b-1); adj[b-1].pb(a-1);}
#define fill_direct(adj,m) for(ll i=0;i<m;i++) {ll a, b; scanf("%lld %lld",&a,&b); adj[a-1].pb(b-1);}
#define StarBurstStream ios_base::sync_with_stdio(false); cin.tie(0); //cout.tie(0);
#define pi 3.1415926535897L
#define db long double  /* print with %Lf */
#define EPS 1e-9
#define flu fflush(stdout)
#define imp {cout<<"No\n"; return 0;}
#define yup {cout<<"Yes\n"; return 0;}
#define debug_vec(vec,n) {rep(idxi,n) cout<<vec[idxi]<<" "; cout<<"\n";}
#define debug_pvec(vec,n) {rep(idxi,n) cout<<vec[idxi].fi<<"-"<<vec[idxi].se<<"  "; cout<<"\n";}
#define debug_set(seta) {cout<<seta.size()<<"\n"; for(auto idxi:seta) cout<<idxi<<" "; cout<<"\n";}
#define debug_map(mappa) {cout<<mappa.size()<<"\n";for(auto idxi:mappa) cout<<idxi.fi<<"-"<<idxi.se<<"  "; cout<<"\n";}
#define debug_vecvec(vec,n) {rep(idxi,n) {for(auto idxi2:vec[idxi]) cout<<idxi2<<" "; cout<<"\n";}}
 
// LOOK AT THESE BEFORE SUBMISSION
// LOOK AT THESE BEFORE SUBMISSION
// ============================================================
// Nmax value and is index access offset taking it beyond Nmax.
// Precision error in case of real numbers.
// N vs N2 chosen correctly.
// Modulo applied everywhere.
// Flush in case of interactive.
// Don't erase value in multiset.
// Check for array indices out of bound (in pre or suff sums).
// Correct return value for functions.
// Confirm the letter case of yes and no.
// Dont paste code two times in the text file.
// ============================================================


int main() {

    get2(h,w);

    vector<string> A(h);
    rep(i,h) {
        gets(s);
        A[i] = s;
    }

    deque<pll> q;
    vector<vv<ll>> dist(h, vv<ll>(w,INF));

    if(A[0][0]=='.') {
        dist[0][0] = 0;
    } else {
        dist[0][0] = 1;
    }
    
    q.push_front({0,0});

    while(!q.empty()) {
        pll t = q.front(); q.pop_front();
        ll x = t.fi, y = t.se;

        if(x+1<h) {

            ll cost = (A[x][y]=='.' && A[x+1][y]=='#');
            if(dist[x+1][y] > dist[x][y] + cost) {
                dist[x+1][y] = dist[x][y] + cost;
                if(cost==1) q.push_back({x+1,y});
                else q.push_front({x+1,y});
            }

        }

        if(y+1<w) {
            ll cost = (A[x][y]=='.' && A[x][y+1]=='#');
            if(dist[x][y+1] > dist[x][y] + cost) {
                dist[x][y+1] = dist[x][y] + cost;
                if(cost==1) q.push_back({x,y+1});
                else q.push_front({x,y+1});
            }
        }
    }

    printf("%lld\n", dist[h-1][w-1]);

    return 0;  
}   


Measured memory_bytes: 384