#include <bits/stdc++.h>
using namespace std;
const int K = 1e2 + 5,N = 4e4 + 5,M = 2e6 + 5;
typedef long long ll;
const int inf = 0x7f7f7f7f;
const ll llinf = 0x7f7f7f7f7f7f7f7f;
namespace Flow{ // 要根据流量和费用范围，修改代码中的 inf !
	int fir[N],nxt[M],to[M],w[M],ect = 1,id[M];
	inline void addedge(int u1,int v1,int w1)
	{
		nxt[++ect] = fir[u1];fir[u1] = ect;to[ect] = v1;w[ect] = w1;
	}
	inline void ins(int u1,int v1,int w1) { addedge(u1,v1,w1);addedge(v1,u1,0);}
	int dep[N],cur[N];
	int tot; 
	inline void Clr(int _n)
	{
		tot = _n;ect = 1;
		for(int i = 0;i <= tot;i++) fir[i] = 0;
	}
	bool bfs(int S,int T)
	{
		for(int i = 0;i <= tot;i++) dep[i] = inf,cur[i] = fir[i];
		queue<int>Q;Q.push(S);dep[S] = 0;
		while(!Q.empty())
		{
			int x = Q.front();Q.pop();
			for(int i = fir[x],y;y = to[i],i;i = nxt[i])
				if(w[i] && dep[y] > dep[x] + 1)
					dep[y] = dep[x] + 1,Q.push(y);
		}
		return dep[T] < 1e9;
	}
	int dfs(int u,int t,int limit)
	{
		if(u == t || !limit) return limit;
		int flow = 0,f;
		for(int i = cur[u],v;v = to[i],i;i = nxt[i])
		{
			cur[u] = i;
			if((dep[v] == dep[u] + 1) && w[i] && (f = dfs(v,t,min(limit,w[i]))))
			{
				flow += f;
				limit -= f;
				w[i] -= f;
				w[i ^ 1] += f;
				if(!limit) break;
			}
		}
		return flow;
	}
	inline int dinic(int S,int T)
	{
		int res = 0;
		while(bfs(S,T)) res += dfs(S,T,inf);
		return res;
	}
} // 调用 Flow::Clr 传入总点数！
int n,m;
char s[K][K];
struct Node{
	int tp,l,r,x;
	Node(){}
	Node(const int _tp,const int _l,const int _r,const int _x):
		tp(_tp),l(_l),r(_r),x(_x){}
};
Node T[N];
int tot;
int main() {
	scanf("%d%d",&n,&m);int ans = n * m;
	for(int i = 1;i <= n;i++) scanf("%s",s[i] + 1);
	for(int i = 1;i <= n;i++) {
		s[i][0] = '1';s[i][m + 1] = '4';
		int lst = -1,lstp = 0;
		for(int j = 0;j <= m + 1;j++) {
			if(s[i][j] == 'x') lst = -1,--ans;
			if(s[i][j] >= '1' && s[i][j] <= '4') {
				int p = (s[i][j] - '1') >> 1;
				if(lst >= 0 && ((j&1) ^ (lst&1) ^ p ^ lstp))
					T[++tot] = Node(0,lst + 1,j - 1,i);
				lstp = p;lst = j;
			}
		}
	}
	for(int j = 1;j <= m;j++) {
		s[0][j] = '1';s[n + 1][j] = '4';
		int lst = -1,lstp = 0;
		for(int i = 0;i <= n + 1;i++) {
			if(s[i][j] == 'x') lst = -1;
			if(s[i][j] >= '1' && s[i][j] <= '4') {
				int p = (s[i][j] - '1') & 1;
				if(lst >= 0 && ((i&1) ^ (lst&1) ^ p ^ lstp))
					T[++tot] = Node(1,lst + 1,i - 1,j);
				lstp = p;lst = i; 
			}
		}
	}
	for(int i = 1;i <= tot;i++) {
		auto Fail = [&]() { puts("-1");exit(0);};
		if(T[i].l > T[i].r) Fail();
		if(T[i].tp == 0) {
			bool flg = 1;
			for(int t = T[i].l;t <= T[i].r;t++)
				if(s[T[i].x][t] != 'o') flg = 0;
			if(flg) Fail();
		} else {
			bool flg = 1;
			for(int t = T[i].l;t <= T[i].r;t++)
				if(s[t][T[i].x] != 'o') flg = 0;
			if(flg) Fail();
		}
	}
	ans -= tot;
	Flow::Clr(tot + 2);
	for(int i = 1;i <= tot;i++)
		if(T[i].tp == 0)
			for(int j = 1;j <= tot;j++)
				if(T[j].tp == 1)
					if(T[i].l <= T[j].x && T[j].x <= T[i].r && T[j].l <= T[i].x && T[i].x <= T[j].r && s[T[i].x][T[j].x] == '.')
						Flow::ins(i,j,1);
	int S = tot + 1,TT = tot + 2;
	for(int i = 1;i <= tot;i++) if(T[i].tp == 0) Flow::ins(S,i,1); else Flow::ins(i,TT,1);
	ans += Flow::dinic(S,TT);
	cout << ans << endl;
	return 0;
}