#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
#define int long long
//#define int double
typedef pair<int,int> pii;
typedef vector<pii> vii;
typedef vector<int> vi;
typedef vector<bool> vb;
#define FOR(i,a) for(int i=0;i<(a);i++)
#define FORE(i,a,b) for(int i=(a);i<(b);i++)
#define all(x) x.begin(),x.end()
#define fi first
#define se second
#define pb push_back
#define sp <<" "<<
#define cont(x) for(auto el:x) cout<<el<<' ';cout<<endl;
#define contp(x) for(auto el:x) cout<<el.fi<<'-'<<el.se<<' ';cout<<endl;
#define DEBUG(x) cout<<#x sp x<<endl;
#define carp(x,y) ((x%MOD)*(y%MOD))%MOD
#define topla(x,y) ((x%MOD)+(y%MOD))%MOD
#define mid (double)(l+r)/2
const int MAXN=1050;
const int INF=1e9+7;
int n,m;
int dp[MAXN][MAXN];
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
cin>>n>>m;
vector<string> grid(n);
FOR(i,n) cin>>grid[i];
int ans=INF;
FOR(i,n){
for(int mask=0;mask<(1<<m);mask++){
dp[i][mask]=INF;
//1--> verticaldan gel
//0--> yataydan gel
int cost=0;
bool f=false;
for(int bt=0;bt<m;bt++){
if(grid[i][bt]=='.'){
if(f) cost++;
f=false;
}
else{
if(mask&(1<<bt)){
if(i==0 or grid[i-1][bt]!='#') cost++;
}
else f=true;
}
}
if(f) cost++;
dp[i][mask]=min(dp[i][mask],(i-1>=0?dp[i-1][mask]:0)+cost);
if(i==n-1) ans=min(ans,dp[i][mask]);
}
}
cout<<ans<<endl;
}
