#include <bits/stdc++.h>
using namespace std;
#define int long long   // <-----!!!!!!!!!!!!!!!!!!!

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n)-1;i>=0;i--)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define printV(v) for(auto&& x : v){cout << x << " ";} cout << endl
#define printVV(vv) for(auto&& v : vv){for(auto&& x : v){cout << x << " ";}cout << endl;}
#define printP(p) cout << p.first << " " << p.second << endl
#define printVP(vp) for(auto&& p : vp) printP(p);

typedef long long ll;
typedef pair<int, int> Pii;
typedef tuple<int, int, int> TUPLE;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<Pii> vp;
const int inf = 1e9;
const int mod = 1e9 + 7;
template<typename T> using Graph = vector<vector<T>>;

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

const int MAX_V = 2510;
vector<edge> G[MAX_V];
int level[MAX_V];
int iter[MAX_V];

void add_edge(int from, int to, int cap) {
    G[from].emplace_back((edge){to, cap, (int)G[to].size()});
    G[to].emplace_back((edge){from, 0, (int)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();
        for (int i = 0; i < G[v].size(); i++) {
            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 H, W;

// N, E, S, W
const int dx[4] = {-1, 0,  1,  0};
const int dy[4] = { 0, 1,  0, -1};

bool inside(int x, int y) {
    return 0 <= x && x < H && 0 <= y && y < W;
}

int node(int i, int j) {
    return i * W + j;
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    cin >> H >> W;
    vector<string> choco(H);
    rep(i, H) cin >> choco[i];

    const int s = H * W, t = s + 1;
    int nb = 0, nw = 0;
    // s -> odd -> even -> t
    rep(i, H) {
        rep(j, W) {
            if (choco[i][j] == 'b') {
                nb++;
            } else if (choco[i][j] == 'w') {
                nw++;
            }

            if ((i + j) % 2) {
                add_edge(s, node(i, j), 1);
                rep(k, 4) {
                    int ni = i + dx[k], nj = j + dy[k];
                    if (inside(ni, nj) && ((choco[i][j] == 'b' && choco[ni][nj] == 'w') || (choco[i][j] == 'w' && choco[ni][nj] == 'b'))) {
                        add_edge(node(i, j), node(ni, nj), 1);
                    }
                }
            } else {
                add_edge(node(i, j), t, 1);
            }
        }
    }

    int match = max_flow(s, t);
    int ans = 100 * match;
    nb -= match, nw -= match;
    ans += 10 * min(nb, nw);
    ans += max(nb - nw, nw - nb);
    cout << ans << endl;
}