#include<bits/stdc++.h>
using namespace std;
int main()
{
	ios_base::sync_with_stdio(false);
	const int inf=0x3f3f3f3f;
	int n,m;
	cin>>n>>m;
	vector<string> s(n+5);
	for(int i=1;i<=n;i++)
	{
		cin>>s[i];
		s[i]=' '+s[i]+' ';
	}
	s[0]=s[n+1]=string(m+5,' ');
	const int N=(n+1)*(m+1)*2;
	vector<vector<pair<int,int>>> G(N+5);
	auto addedge=[&](int u,int v,int w)
	{
//		cerr<<"addedge "<<u<<' '<<v<<' '<<w<<endl;
		G[u].emplace_back(v,w);
	};
	auto hs=[&](int x,int y,int ty)
	{
		return ty*(n+1)*(m+1)+x*(m+1)+y+1;
	};
	for(int i=0;i<=n;i++)
	{
		for(int j=0;j<=m;j++)
		{
			{
				int w=(s[i][j]=='#')+(s[i][j+1]=='#')+(s[i+1][j]=='#')+(s[i+1][j+1]=='#');
				addedge(hs(i,j,0),hs(i,j,1),w);
			}
			if(i<n)
			{
				//down
				int w=(s[i+1][j]=='#')+(s[i+1][j+1]=='#');
				addedge(hs(i,j,1),hs(i+1,j,0),-w);
				addedge(hs(i+1,j,1),hs(i,j,0),-w);
			}
			if(j<m)
			{
				//right
				int w=(s[i][j+1]=='#')+(s[i+1][j+1]=='#');
				addedge(hs(i,j,1),hs(i,j+1,0),-w);
				addedge(hs(i,j+1,1),hs(i,j,0),-w);
			}
		}
	}
	int S=hs(0,0,0),T=hs(n,m,1);
	vector<int> dis(N+5,inf),inq(N+5);
	dis[S]=0;
	queue<int> q;
	q.push(S);inq[S]=1;
	while(not q.empty())
	{
		int u=q.front();q.pop();
		inq[u]=0;
//		cerr<<"go "<<u<<' '<<dis[u]<<endl;
		for(auto [v,w]:G[u])
		{
			if(dis[v]>dis[u]+w)
			{
				dis[v]=dis[u]+w;
				if(inq[v]==0)
				{
					inq[v]=1;
					q.push(v);
				}
			}
		}
	}
	cout<<dis[T]<<endl;
/*	
	for(int i=0;i<=n;i++)
		for(int j=0;j<=m;j++)
		{
			cerr<<i<<' '<<j<<' '<<0<<' '<<dis[hs(i,j,0)]<<"\n";
			cerr<<i<<' '<<j<<' '<<1<<' '<<dis[hs(i,j,1)]<<"\n";
		}
*/	
	return 0;
}