#include <bits/stdc++.h>

#define int int64_t
using namespace std;

int N,M;
string mp[512];
int id[512][512];
bool is_inside(array<int,2> p) {
	return (0<=p[0] && p[0]<N && 0<=p[1] && p[1]<M);
}
array<int,2> beam(array<int,2> p, array<int,2> d) {
	if(!is_inside(p)) {
		d[0]=-d[0];
		d[1]=-d[1];
	} else if(mp[p[0]][p[1]] == '\\') {
		swap(d[0],d[1]);
	} else if(mp[p[0]][p[1]] == '/') {
		swap(d[0],d[1]);
		d[0]=-d[0];
		d[1]=-d[1];
	} else if(mp[p[0]][p[1]] == '#') {
		return {-1,-1};
	} else if(mp[p[0]][p[1]] == 'V' || mp[p[0]][p[1]] == 'H') {
		return {id[p[0]][p[1]],d[0]?0:1};
	}
	p[0]+=d[0];
	p[1]+=d[1];
	return beam(p,d);
}
int n;
// H=0
// V=1
vector<vector<array<int,2> > > g;
vector<int> dc;
vector<int> og;
array<int,2> dfs(int u, int d) {
	dc[u]=d;
	int num=1;
	int nd=og[u]^d;
	for(auto [v,dd]: g[u]) {
		if(dc[v]==-1) {
			auto [a,b] = dfs(v,d^dd);
			if(a==-1) return {-1,-1};
			num+=a;
			nd+=b;
		} else if(dc[v]!=(d^dd)) {
			return {-1,-1};
		}
	}
	return {num,nd};
}
signed main() {
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	cin>>N>>M;
	for(int i=0; i<N; ++i) cin>>mp[i];
	for(int i=0; i<N; ++i) {
		for(int j=0; j<M; ++j) if(mp[i][j]=='V' || mp[i][j]=='H') {
			id[i][j]=n++;
		}
	}
	g.resize(n);
	dc.resize(n,-1);
	og.resize(n,-1);
	vector<array<int,2> > forced;
	for(int i=0; i<N; ++i) {
		for(int j=0; j<M; ++j) if(mp[i][j]=='V' || mp[i][j]=='H') {
			int id0 = id[i][j];
			og[id0] = (mp[i][j]=='V');
			{
				auto [id1,d] = beam({i+1,j},{1,0});
				if(id1!=-1) g[id0].push_back({id1,d});
				else forced.push_back({id0,0});
			}
			{
				auto [id1,d] = beam({i-1,j},{-1,0});
				if(id1!=-1) g[id0].push_back({id1,d});
				else forced.push_back({id0,0});
			}
			{
				auto [id1,d] = beam({i,j+1},{0,1});
				if(id1!=-1) g[id0].push_back({id1,!d});
				else forced.push_back({id0,1});
			}
			{
				auto [id1,d] = beam({i,j-1},{0,-1});
				if(id1!=-1) g[id0].push_back({id1,!d});
				else forced.push_back({id0,1});
			}
		}
	}
	int ans=0;
	for(auto [i,d]:forced) {
		if(dc[i]==-1) {
			auto [num,nd] = dfs(i,d);
			ans+=nd;
		} else if(dc[i]!=d) {
			cout<<-1<<endl;
			return 0;
		}
	}
	for(int i=0; i<n; ++i) if(dc[i]==-1) {
		auto [num,nd] = dfs(i,0);
		if(num==-1) {
			cout<<-1<<endl;
			return 0;
		}
		ans+=min(nd,num-nd);
	}
	cout<<ans<<endl;
	return 0;
}