#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define pb push_back
#define SZ(a) ((int)a.size())
#define ALL(v) v.begin(), v.end()

int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};

int n, m;
pii dp[505][505][4];
string mp[505];
int idx[505][505];
pii get(int i, int j, int k) {
    if (dp[i][j][k].X != -1)
        return dp[i][j][k];
    int ni = i + dx[k], nj = j + dy[k];
    if (ni <= 0 || ni > n || nj <= 0 || nj > m)
        return dp[i][j][k] = get(ni, nj, k ^ 2);
    char c = mp[ni][nj];
    if (c == '#')
        return dp[i][j][k] = {0, 0};
    if (c == '/')
        return dp[i][j][k] = get(ni, nj, k ^ 1); 
    if (c == '\\')
        return dp[i][j][k] = get(ni, nj, k ^ 3);
    if (c == '.')
        return dp[i][j][k] = get(ni, nj, k);
    assert(c == 'H' || c == 'V');
    return dp[i][j][k] = {idx[ni][nj], (k & 1)};
}

const int N = 5e5 + 5;
int org[N], g[N], cst[N];
pii loc[N];
int f(int x) { return g[x] = (g[x] == x ? x : f(g[x])); }
void mg(int a, int b) {
    // cerr << "mg " << a << " " << b << endl;
    a = f(a), b = f(b);
    g[a] = b;
}
vector<int> v[N];
int clr[N];
vector<int> cv[2];

void qt(int ans) {
    cout << ans << endl;
    exit(0);
}

void dfs(int now) {
    cv[clr[now]].pb(now);
    for (int k : v[now]) {
        if (clr[k] == -1)
            clr[k] = !clr[now], dfs(k);
        else if (clr[k] == clr[now])
            qt(-1);
    }
}

const int INF = 1e9;

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
        string s;
        cin >> s;
        mp[i] = "." + s;
    }
    for (int i = 0; i <= n + 1; i++)
        for (int j = 0; j <= m + 1; j++) {
            idx[i][j] = -1;
            for (int k = 0; k < 4; k++)
                dp[i][j][k] = {-1, -1};
        }
    int it = 0;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            char c = mp[i][j];
            if (c == 'H' || c == 'V') {
                idx[i][j] = ++it;
                loc[it] = {i, j};
                org[it] = (c == 'H'); 
            }
        }
    for (int i = 0; i <= 2 * it + 1; i++)
        g[i] = i;
    mg(0, 1);
    for (int i = 1; i <= it; i++)
        for (int k = 0; k < 4; k++) {
            auto p = get(loc[i].X, loc[i].Y, k); 
            // cerr << i <<  " " << k << " " << p.X << " " << p.Y << endl;
            mg(2 * i + (k & 1), 2 * p.X + p.Y);
        }
    vector<int> blk;
    for (int i = 2; i <= 2 * it + 1; i++)
        if (f(i) == i) {
            blk.pb(i);
            // cerr << i << endl;
        }
    for (int i = 1; i <= it; i++) {
        int g0 = f(2 * i);
        int g1 = f(2 * i + 1);
        if (g0 == g1)
            qt(-1);
        v[g0].pb(g1);
        v[g1].pb(g0);
        cst[g0] += (org[i] != 0);
        cst[g1] += (org[i] != 1);
    }
    memset(clr, -1, sizeof(clr));
    int ans = 0;
    for (int x : blk)
        if (clr[x] == -1) {
            // cerr << "go " << x << endl;
            cv[0].clear(); cv[1].clear();
            clr[x] = 0;
            dfs(x);
            int tmp = INF;
            for (int i = 0; i < 2; i++) {
                int tt = 0; 
                for (int y : cv[i])
                    if (f(y) == f(0))
                        tt = INF;
                    else
                        tt += cst[y];
                tmp = min(tmp, tt);
            }
            if (tmp >= INF)
                qt(-1);
            ans += tmp;
        }
    cout << ans << endl;
}