#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define BIT(mask,x) ((mask)>>(x)&(1))
#define MASK(x) ((ll)(1)<<(x))
#define all(datastructure) datastructure.begin(),datastructure.end()
void compress(vector<int>&x){
x.resize(unique(all(x))-x.begin());
}
template <class T1 , class T2>
bool minU(T1 &a, T2 b){
if (a>b) return a = b , true;
return false;
}
template <class T1 , class T2>
bool maxU(T1 &a, T2 b){
if (a<b) return a = b,true;
return false;
}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
int Rand(int l , int r){
return uniform_int_distribution<int> (l,r)(rng);
}
const int maxn = 1e3;
const int maxm = 10;
char c[maxn+2][maxm+2];
int dp[maxn+2][MASK(maxm)];
int tmp[MASK(maxm)] , add[maxn+2][MASK(maxm)] ;
bool go[MASK(maxm)];
int numrow , numcol;
bool ok(int id , int mask){
for (int i = 0; i < numcol; ++i){
if (BIT(mask,i) && c[id][i]=='.') return false;
}
return true;
}
int calc(int id , int mask){
int ngang = 0 , ans = 0;
for (int i = 0; i < numcol; ++i){
if (BIT(mask,i)){
ans += ngang;
ngang = 0;
}
else {
if (c[id][i]=='.'){
ans += ngang;
ngang = 0;
}
else {
if (i==0||BIT(mask,i-1)||c[id][i-1]=='.') ngang = 1;
}
}
}
ans += ngang;
return ans;
}
void upstate(int id){
for (int mask = 0; mask < MASK(numcol); ++mask){
tmp[mask] = dp[id-1][mask];
}
for (int mask = 0; mask < MASK(numcol); ++mask){
for (int j = 0; j < numcol; ++j){
if (BIT(mask,j))
tmp[mask] = min(tmp[mask] , tmp[mask^MASK(j)]+1);
}
}
for (int mask = MASK(numcol); mask >= 0; --mask){
for (int j = 0; j < numcol; ++j){
if (!BIT(mask,j))
tmp[mask] = min(tmp[mask] , tmp[mask|MASK(j)]);
}
}
return;
}
int32_t main(){
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
#define name "main"
if (fopen(name".inp","r")){
freopen(name".inp","r",stdin);
freopen(name".out","w",stdout);
}
cin >> numrow >> numcol;
for (int i = 1; i <= numrow; ++i){
for (int j = 0; j < numcol; ++j){
cin >> c[i][j];
}
}
memset(dp,0x3f,sizeof dp);
dp[0][0] = 0;
for (int i = 1; i <= numrow; ++i){
for (int mask = 0; mask < MASK(numcol); ++mask) {
add[i][mask] = calc(i,mask);
go[mask] = ok(i,mask);
}
upstate(i);
for (int mask = 0; mask < MASK(numcol); ++mask){
if (go[mask]) dp[i][mask] = tmp[mask] + add[i][mask];
}
}
int ans = numrow*numcol;
for (int mask = 0; mask < MASK(numcol); ++mask)
{
ans = min(ans , dp[numrow][mask]);
int id = 3;
// cout << dp[id][mask] << "\n";
// for (int j = 0; j < numcol; ++j) cout << BIT(mask,j);
// cout << '\n';
}
cout << ans;
}
