#include<bits/stdc++.h>
using namespace std;
#define foru(i,a,b) for(int i=(a); i<=(b); ++i)
#define ford(i,a,b) for(int i=(a); i>=(b); --i)
#define rep(i,a) for(int i=0; i<(a); ++i)
#define sz(a) (int)(a).size()
#define all(a) (a).begin(),(a).end()
#define bit(s,i) (((s)>>(i))&1)
#define ii pair<int,int>
#define vi vector<int>
#define vii vector<ii>
#define fi first
#define se second
#define ll long long
#define eb emplace_back
#define pb push_back
#define __builtin_popcount __builtin_popcountll
#define _ << " " <<
template <class X, class Y> bool maxi(X &x, Y y){return x<y?x=y,true:false;}
template <class X, class Y> bool mini(X &x, Y y){return x>y?x=y,true:false;}
const int N=1010;
const int M=10;
const int INF=1e9;
int n,m,g[M+1][1<<M];
char a[N][M];
void solve(){
cin>>n>>m;
foru(i,1,n) foru(j,1,m) cin>>a[i][j];
memset(g,0x3f,sizeof(g));
g[0][0]=0;
foru(i,1,n){
foru(j,0,m-1) rep(msk,1<<m){
if(a[i][j+1]=='#'){
if(j>0 && a[i][j]=='#' && !bit(msk,j-1)) mini(g[j+1][msk&(~(1<<j))], g[j][msk]);
if(a[i-1][j+1]=='#' && bit(msk,j)) mini(g[j+1][msk], g[j][msk]);
mini(g[j+1][msk|(1<<j)], g[j][msk]+1);
mini(g[j+1][msk&(~(1<<j))], g[j][msk]+1);
} else{
mini(g[j+1][msk&(~(1<<j))], g[j][msk]);
}
}
rep(msk,1<<m){
g[0][msk]=g[m][msk];
}
foru(j,1,m) rep(msk,1<<m){
g[j][msk]=INF;
}
}
int res=INF;
rep(msk,1<<m) mini(res,g[0][msk]);
cout<<res<<'\n';
}
int32_t main(){
#define task "test"
if(fopen(task".inp", "r")){
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
cin.tie(0)->sync_with_stdio(0);
int tc=1; //cin>>tc;
foru(i,1,tc){
solve();
}
}
