#include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <stack>
#include <algorithm>
#include <string>
#include <queue>
#include <cctype>
#include <cstring>
#include <iomanip>
#include <deque>
#include <random>
#include <sstream>
// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")
// #pragma GCC optimize("Ofast","inline","no-stack-protector")
using namespace std;
#define file(name) freopen(name".inp","r",stdin);\
freopen(name".out","w",stdout);
#define TIME (1.0*clock()/CLOCKS_PER_SEC)
#define all(a) a.begin(),a.end()
#define all1(a) a+1,a+n+1
#define ll long long
const long long INF=1e18;
const long long MOD=1e9+7;
const long long MODD=998244353; // 998244353
const int maxN=1e6+9;
const short LOG=20;
//------------------------
void solve();
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
// file("boat");
int t;
// cin >> t;
t=1;
while (t--){
solve();
}
return 0;
}
/// -------------- PROBLEM SOLUION --------------------
#define int ll
char a[1009][19];
int n,m;
long long dp[1009][1100];
long long cost(int i, int mask){
long long ans=0;
for (int j=1; j<=m; j++){
if (((mask>>(j-1))&1) == 0) {
if (a[i][j]=='.') continue;
if (j==1 || a[i][j-1]=='.' || ((mask>>(j-2))&1)) ans++;
}
}
return ans;
}
void solve(){
cin >> n >> m;
for (int i=1; i<=n; i++){
for (int j=1; j<=m; j++){
cin >> a[i][j];
}
}
// dp[i][mask] bit[j] = 0/1 la hang j duoc dan hoac cot j duoc dan
memset(dp,0x3f,sizeof dp);
dp[0][0]=0;
for (int i=1; i<=n; i++){
for (int mask=0; mask<(1<<m); mask++){
int ok=1;
for (int j=1; j<=m; j++){
if (((mask>>(j-1))&1) && a[i][j]=='.') ok=0;
}
if (!ok) continue;
// for bit con
for (int nmask = mask;; nmask = (nmask - 1) & mask){
dp[i][mask]=min(dp[i][mask],dp[i-1][nmask] + __builtin_popcount(nmask^mask));
if (!nmask) break;
}
dp[i][mask]+=cost(i,mask);
for (int nmask = mask;; nmask = (nmask - 1) & mask){
dp[i][nmask]=min(dp[i][nmask],dp[i][mask]);
if (!nmask) break;
}
}
}
long long ans=INF;
for (int mask=0; mask<(1<<m); mask++){
ans=min(ans,dp[n][mask]);
// cout << dp[n][mask] << "\n";
}
cout << ans;
}
