#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 2502;

char c[52][52];
vector<P> od,ev;
vector<int> kind1,kind2;

struct edge
{
	int to,cap,rev;
};

vector<edge> G[MAX_N];
int level[MAX_N];
int iter[MAX_N];

void add_edge(int from,int to,int cap)
{
	G[from].push_back((edge){to,cap,G[to].size()});
	G[to].push_back((edge){from,0,G[from].size()-1});
}

void bfs(int s)
{
	memset(level,-1,sizeof(level));
	queue<int> que;
	level[s] = 0;
	que.push(s);
	while(!que.empty()){
		int v = que.front();
		que.pop();
		rep(i,G[v].size()){
			edge &e = G[v][i];
			if(e.cap > 0 && level[e.to] < 0){
				level[e.to] = level[v] + 1;
				que.push(e.to);
			}
		}
	}
}

int dfs(int v,int t,int f)
{
	if(v==t){
		return f;
	}
	for(int &i = iter[v];i<G[v].size();i++){
		edge &e = G[v][i];
		if(e.cap > 0 && level[v] < level[e.to]){
			int d = dfs(e.to,t,min(f,e.cap));
			if(d>0){
				e.cap -= d;
				G[e.to][e.rev].cap += d;
				return d;
			}
		}
	}
	return 0;
}

int max_flow(int s,int t)
{
	int flow = 0;
	for(;;){
		bfs(s);
		if(level[t]<0){
			return flow;
		}
		memset(iter,0,sizeof(iter));
		int f;
		while((f=dfs(s,t,INF)) > 0){
			flow += f;
		}
	}
}


int main()
{
    int n,m;
    cin >> n >> m;
    int wnum = 0,bnum = 0;
    rep(i,n){
        rep(j,m){
            cin >> c[i][j];
            if(c[i][j] == 'w'){
                if((i+j)%2){
                    od.pb(P(i,j));
                    kind1.pb(0);
                }else{
                    ev.pb(P(i,j));
                    kind2.pb(0);
                }
                wnum++;
            }else if(c[i][j] == 'b'){
                if((i+j)%2){
                    od.pb(P(i,j));
                    kind1.pb(1);
                }else{
                    ev.pb(P(i,j));
                    kind2.pb(1);
                }
                bnum++;
            }
        }
    }
    int l = (int)od.size();
    int r = (int)ev.size();
    rep(i,l){
        add_edge(0,i+1,1);
    }
    rep(i,l){
        rep(j,r){
            P p1 = od[i];
            P p2 = ev[j];
            if(kind1[i] != kind2[j]){
                if(abs(p1.fi-p2.fi) + abs(p1.se-p2.se) == 1){
                    add_edge(i+1,l+j+1,1);
                }
            }
        }
    }
    rep(i,r){
        add_edge(l+i+1,l+r+1,1);
    }
    int f = max_flow(0,l+r+1);
    cout << abs(bnum-wnum) + 10 * (min(wnum,bnum) - f) + 100 * f << endl;
    return 0;
}