#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
#include <random>
#include <chrono>
#include <fstream>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, m;
cin>>n>>m;
vector<string> vect(n+1);
for (int i=1; i<=n; ++i)cin>>vect[i];
vector<vector<vector<int> > > dp(n+1, vector<vector<int> >(m, vector<int>((1<<m), LLONG_MAX/2)));
for (int mask=0; mask<(1<<m); ++mask)dp[0][m-1][mask]=0;
for (int i=1; i<=n; ++i)for (int j=0; j<m; ++j)for (int mask=0; mask<(1<<m); ++mask){
if (vect[i][j]=='#'){
if (mask&(1<<j)){
if (!j){
dp[i][j][mask]=min(dp[i][j][mask], dp[i-1][m-1][mask^(1<<j)]+1);
if (i!=1&&vect[i-1][j]=='#')dp[i][j][mask]=min(dp[i][j][mask], dp[i-1][m-1][mask]);
}
else{
dp[i][j][mask]=min(dp[i][j][mask], dp[i][j-1][mask^(1<<j)]+1);
if (i!=1&&vect[i-1][j]=='#')dp[i][j][mask]=min(dp[i][j][mask], dp[i][j-1][mask]);
}
}
else{
if (!j)dp[i][j][mask]=min(dp[i-1][m-1][mask], dp[i-1][m-1][mask|(1<<j)])+1;
else{
dp[i][j][mask]=min(dp[i][j-1][mask], dp[i][j-1][mask|(1<<j)])+1;
if (vect[i][j-1]=='#'&&!(mask&(1<<(j-1))))dp[i][j][mask]=min(dp[i][j-1][mask], dp[i][j-1][mask|(1<<j)]);
}
}
}
else{
if (!j)dp[i][j][mask]=min(dp[i-1][m-1][mask], dp[i-1][m-1][mask^(1<<j)]);
else dp[i][j][mask]=min(dp[i][j-1][mask], dp[i][j-1][mask^(1<<j)]);
}
}
cout<<*min_element(dp[n][m-1].begin(), dp[n][m-1].end());
}
