//雪花飄飄北風嘯嘯
//天地一片蒼茫
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
#define ll long long
#define ii pair<ll,ll>
#define iii pair<ii,ll>
#define fi first
#define se second
#define endl '\n'
#define debug(x) cout << #x << " is " << x << endl
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define lb lower_bound
#define up upper_bound
#define rep(x,start,end) for(auto x=(start)-((start)>(end));x!=(end)-((start)>(end));((start)<(end)?x++:x--))
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()
#define indexed_set tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>
//change less to less_equal for non distinct pbds, but erase will bug
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
int n,m;
string grid[1005];
int memo[1005][10][1024][2];
int dp(int p1,int p2,int mask,int prev){
if (p2==m) return dp(p1+1,0,mask,0);
if (p1==n) return 0;
if (memo[p1][p2][mask][prev]!=-1) return memo[p1][p2][mask][prev];
int ans;
if (grid[p1][p2]=='.'){
if (mask&(1<<p2)) mask^=(1<<p2); //remove hori line
ans=dp(p1,p2+1,mask,0); //also no vert line
}
else{
if (prev==1 && mask&(1<<p2)){
ans=min(dp(p1,p2+1,mask^(1<<p2),prev),
dp(p1,p2+1,mask,0));
}
else if (prev==1 || mask&(1<<p2)){
ans=dp(p1,p2+1,mask,prev);
}
else{
ans=min(dp(p1,p2+1,mask|(1<<p2),0)+1,
dp(p1,p2+1,mask,1)+1);
}
}
return memo[p1][p2][mask][prev]=ans;
}
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin.exceptions(ios::badbit | ios::failbit);
cin>>n>>m;
rep(x,0,n) cin>>grid[x];
memset(memo,-1,sizeof(memo));
cout<<dp(0,0,0,0)<<endl;
}
