#include <bits/stdc++.h>
using namespace std;
#define int long long
const int inf = 1e10;
char mat[1005][15];
void solve(){
int n, m; cin >> n >> m;
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++) cin >> mat[i][j];
}
vector <int> dp(1 << m, inf), novi(1 << m);
dp[0] = 0;
for(int i = 0; i < n; i++){
for(int j = 0; j < m; j++){
for(int k = 0; k < (1 << m); k++){
if(k & (1 << j)) {
if(mat[i][j] == '.') novi[k] = inf;
else novi[k] = min(dp[k], dp[k ^ (1 << j)] + 1);
}
else {
novi[k] = min(dp[k], dp[k ^ (1 << j)]);
if(mat[i][j] == '#' && (j == 0 || (k & (1 << (j - 1))) || mat[i][j - 1] == '.')) novi[k]++;
}
}
dp = novi;
}
}
cout << *min_element(dp.begin(), dp.end()) << " ";
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
}
