照着题解 贺 打的，但是第九个点 TLE，死活卡不过去，也不知道哪锅了，求卡常 / 调锅

#include<bits/stdc++.h>
using namespace std;
#define ll long long
int n,m,mp[25][25];
int mxx,mxy;
int now,lst=1;
ll ans,dp[2][600005];
int sts[2][600005],cnt[2];
struct nd{
	int prv,real;
}arr[600005];
int null[600005],acnt;
const short dob[35]={0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50};
#define db(x) dob[x]
inline void upd(int sta,ll v){
	int id=sta%590027;
	for(int nw=null[id];nw;nw=arr[id].prv) if(sta==sts[now][arr[nw].real]){
		dp[now][arr[nw].real]+=v;
		return;
	}
	sts[now][++cnt[now]]=sta;
	dp[now][cnt[now]]=v;
	arr[++acnt]={null[id],cnt[now]};
	null[id]=acnt;
}
int main(){
	ios::sync_with_stdio(0);
	cin>>n>>m;
	char c;
	for(short i=1;i<=n;i++){
		for(short j=1;j<=m;j++){
			cin>>c;
			if(c=='.'){
				mp[i][j]=1;
				mxx=i,mxy=j;
			}
		}
	}
	dp[0][1]=cnt[0]=1;
	sts[0][1]=0;
	for(short i=1;i<=n;i++){
		for(int j=1;j<=cnt[now];j++) sts[now][j]<<=2;
		for(short j=1;j<=m;j++){
			acnt=0;
			memset(null,0,sizeof(null));
			swap(lst,now);
			cnt[now]=0;
			for(register int k=1;k<=cnt[lst];k++){
				const int st=sts[lst][k];
				const ll as=dp[lst][k];
				const short d=(st>>db(j))&3,r=(st>>db(j-1))&3;
				if(!mp[i][j]){
					if(!d&&!r) upd(st,as);
				}else if(!d&&!r){
					if(mp[i][j+1]&&mp[i+1][j]) upd(st+(1<<db(j-1))+(2<<db(j)),as);
				}else if(!d&&r){
					if(mp[i+1][j]) upd(st,as);
					if(mp[i][j+1]) upd(st-(r<<db(j-1))+(r<<db(j)),as);
				}else if(!r&&d){
					if(mp[i][j+1]) upd(st,as);
					if(mp[i+1][j]) upd(st+(d<<db(j-1))-(d<<db(j)),as);
				}else if(d==1&&r==1){
					register int qwq=1;
					for(short x=j+1;x<=m;x++){
						short tmp=(st>>db(x))&3;
						if(!(tmp==1?++qwq:tmp==2?--qwq:1)){
							upd(st-(int)(1<<db(x))-(1<<db(j))-(1<<db(j-1)),as);
							break;
						}
					}
				}else if(d==2&&r==2){
					register int qwq=1;
					for(short x=j-2;~x;x--){
						short tmp=(st>>db(x))&3;
						if(!(tmp==1?--qwq:tmp==2?++qwq:1)){
							upd(st+(int)(1<<db(x))-(2<<db(j))-(2<<db(j-1)),as);
							break;
						}
					}
				}else if(d==1&&r==2) upd(st-(2<<db(j-1))-(1<<db(j)),as);
				else if(d==2&&r==1) if(i==mxx&&j==mxy) ans+=as;
			}
		}
	}
	cout<<ans<<endl;
	return 0;
}