#include <bits/stdc++.h>
using namespace std;
#define all(v) v.begin(),v.end()
#define eb emplace_back
#define ll long long
#define fi first
#define se second
int t,n,i,m,msk,mask,sub;
const int inf = 1e6;
const int lg = 10;
string s;
int dp[1<<lg][2];
bool now,pre;
int cal(int mask)
{
bool c = 0;
int ans = 0;
while(mask)
{
if(c != (mask & 1))
{
ans += c = (mask & 1);
}
mask>>=1;
}
return ans;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin>>n>>m;
for(mask = 1;mask<(1<<m);mask++)dp[mask][0] = inf;
while(n--)
{
now = !now;
pre = !now;
cin>>s;
msk = bitset<10>(s,0,m,'.','#').to_ulong();
for(mask = 0;mask<(1<<m);mask++)dp[mask][now] = inf;
for(mask = msk;mask;mask = (mask - 1) & msk)
{
for(sub = mask;sub;sub =(sub - 1)&mask)
{
dp[mask][now] = min(dp[mask][now],dp[sub][pre] + __builtin_popcount(mask ^ sub) + cal(msk ^ mask));
}
dp[mask][now] = min(dp[mask][now],dp[0][pre] + __builtin_popcount(mask) + cal(msk ^ mask));
}
dp[0][now] = cal(msk) + dp[0][pre];
for(i = 0;i<m;i++)
{
for(mask = 0;mask<(1<<m);mask++)
{
if((mask >> i & 1)==0)
{
dp[mask][now] = min(dp[mask][now],dp[mask ^ (1<<i)][now]);
}
}
}
}
cout<<dp[0][now];
return 0;
}
