//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define int ll
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
class MinCostMaxFlow
{
	private:
		struct edge
		{
			int u,v,capa,cost;
			edge(int _u,int _v,int _capa,int _cost)
			{
				u=_u;
				v=_v;
				capa=_capa;
				cost=_cost;
			}
			edge(){}
		}E[5005000];
		vector<int> G[101000];
		int p;
		int dist[101000];
		bool inque[101000];
		bool vis[101000];
		int head[100100];
		bool spfa(int s,int t)
		{
			memset(dist,inf,sizeof(dist));
			memset(inque,0,sizeof(inque));
			dist[s]=0;
			inque[s]=1;
			queue<int> q;
			q.push(s);
			while(!q.empty())
			{
				int x=q.front();
				q.pop();
				inque[x]=0;
				for(auto e:G[x])
					if(E[e].capa&&dist[x]+E[e].cost<dist[E[e].v])
					{
						dist[E[e].v]=dist[x]+E[e].cost;
						if(!inque[E[e].v])
						{
							q.push(E[e].v);
							inque[E[e].v]=1;
						}
					}
			}
			return dist[t]<0;
		}
		int cost;
		int dfs(int u,int t,int flow)
		{
			if(u==t)
				return flow;
			vis[u]=1;
			int ans=0;
			for(;head[u]<sz(G[u]);head[u]++)
			{
				int e=G[u][head[u]];
				if(!vis[E[e].v]&&E[e].capa&&dist[E[e].v]==dist[u]+E[e].cost)
				{
					int augflow=dfs(E[e].v,t,min(E[e].capa,flow-ans));
					if(augflow)
					{
						cost+=augflow*E[e].cost;
						E[e].capa-=augflow;
						E[e^1].capa+=augflow;
						ans+=augflow;
					}
				}
			}
			vis[u]=0;
			return ans;
		}
	public:
		void clear()
		{
			p=0;
			for(int i=0;i<101000;i++)
				G[i].clear();
			memset(vis,0,sizeof(vis));
		}
		MinCostMaxFlow()
		{
			clear();
		}
		void addEdge(int u,int v,int capa,int cost)
		{
			G[u].pb(p);
			E[p++]=edge(u,v,capa,cost);
			G[v].pb(p);
			E[p++]=edge(v,u,0,-cost);
		}
		pii mcmf(int s,int t)
		{
			cost=0;
			int ans=0;
			while(spfa(s,t))
			{
				memset(head,0,sizeof(head));
				int x;
				while((x=dfs(s,t,inf)))	ans+=x;
			}
			return mp(ans,cost);
		}
}mcmf;
int n,m;
char grid[105][105];
int nd1[105][105],nd2[105][105];
int tot1,tot2;
signed main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	scanf("%lld%lld",&n,&m);
	for(int i=1;i<=n;i++)
		scanf("%s",grid[i]+1);
	for(int i=1;i<=n;i++)
	{
		vector<int> vp;
		vp.pb(0);
		for(int j=1;j<=m;j++)
			if(isdigit(grid[i][j]))
				vp.pb(j);
		vp.pb(m+1);
		for(int j=1;j<sz(vp);j++)
		{
			int st1=(vp[j-1]?(grid[i][vp[j-1]]>'2'):0);
			int st2=(vp[j]<=m?(grid[i][vp[j]]>'2'):1);
			bool flag=1;
			for(int k=vp[j-1]+1;k<vp[j];k++)
				if(grid[i][k]=='x')
					flag=0;
			if((st1^st2^vp[j-1]^vp[j])&1) if(flag)
			{
				tot1++;
				for(int k=vp[j-1]+1;k<vp[j];k++)
					nd1[i][k]=tot1;
			}
		}
	}
	for(int i=1;i<=m;i++)
	{
		vector<int> vp;
		vp.pb(0);
		for(int j=1;j<=n;j++)
			if(isdigit(grid[j][i]))
				vp.pb(j);
		vp.pb(n+1);
		for(int j=1;j<sz(vp);j++)
		{
			int st1=(vp[j-1]?((grid[vp[j-1]][i]&1)^1):0);
			int st2=(vp[j]<=m?((grid[vp[j]][i]&1)^1):1);
			bool flag=1;
			for(int k=vp[j-1]+1;k<vp[j];k++)
				if(grid[k][i]=='x')
					flag=0;
			if((st1^st2^vp[j-1]^vp[j])&1) if(flag)
			{
				tot2++;
				for(int k=vp[j-1]+1;k<vp[j];k++)
					nd2[k][i]=tot2;
			}
		}
	}
	for(int i=1;i<=tot1;i++)
	{
		mcmf.addEdge(0,i,1,-inf);
		mcmf.addEdge(0,i,inf,0);
	}
	for(int i=1;i<=tot2;i++)
	{
		mcmf.addEdge(i+tot1,tot1+tot2+1,1,-inf);
		mcmf.addEdge(i+tot1,tot1+tot2+1,inf,0);
	}
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++) if(grid[i][j]=='.')
		{
			if(nd1[i][j]&&nd2[i][j])
				mcmf.addEdge(nd1[i][j],tot1+nd2[i][j],1,1);
			else if(nd1[i][j])
				mcmf.addEdge(nd1[i][j],tot1+tot2+1,1,1);
			else if(nd2[i][j])
				mcmf.addEdge(0,tot1+nd2[i][j],1,1);
		}
	ll val=mcmf.mcmf(0,tot1+tot2+1).second;
	val+=1ll*(tot1+tot2)*inf;
	assert(val>=0);
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
			if(grid[i][j]=='x')
				val++;
	if(val<0||val>n*m)
		cout<<"-1\n";
	else
		cout<<n*m-val<<'\n';
	return 0;
}