#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <random>
//#include "util.k"

using namespace std;

//呪文
#define DUMPOUT cout
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

typedef unsigned uint; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<double, double> pdd; typedef pair<string, string> pss;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const pair<_KTy, _Ty>& m) { ostr << "{" << m.first << ", " << m.second << "}"; return ostr; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const map<_KTy, _Ty>& m) { if (m.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { ostr << ", " << *itr; } ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const vector<_Ty>& v) { if (v.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { ostr << ", " << *itr; }	ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const set<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { ostr << ", " << *itr; }	ostr << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const stack<_Ty>& s) { if (s.empty()) { ostr << "{ }"; return ostr; } stack<_Ty> t(s); ostr << "{" << t.top(); t.pop(); while (!t.empty()) { ostr << ", " << t.top(); t.pop(); } ostr << "}";	return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const list<_Ty>& l) { if (l.empty()) { ostr << "{ }"; return ostr; } ostr << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { ostr << ", " << *itr; } ostr << "}"; return ostr; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& istr, pair<_KTy, _Ty>& m) { istr >> m.first >> m.second; return istr; }
template <typename _Ty> istream& operator >> (istream& istr, vector<_Ty>& v) { for (size_t i = 0; i < v.size(); i++) istr >> v[i]; return istr; }
namespace aux { // print tuple
	template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
	template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& value) { os << get<N>(value); } };
}
template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys)-1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); }

#define PI 3.14159265358979323846
#define EPS 1e-11
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define all(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define fake false



class edge {
public:
	int from, to, cost;

	edge() : from(0), to(0), cost(0) {}
	edge(int from, int to) : from(from), to(to), cost(1) {}
	edge(int from, int to, int cost) : from(from), to(to), cost(cost) {}
};

class Dijkstra {

	const int INF;

	// d[k] : 始点 s から頂点 k への最短距離
	// d[k] = min(d[j] + (j から k への辺のコスト) | e = (j, k) in E)
	vector<int> d;
	vector<int> prev;

public:

	typedef pair<int, int> pii;

	// Dijkstra 法 O(|E|log|V|) (負の辺がない場合)
	// G : 隣接リスト, V : 頂点数, s : スタート地点
	// edge の from は使わないので -1 とか入れとく
	Dijkstra(const vector<vector<edge> >& G, int V, int s)
		: INF(1 << 25), d(V, INF), prev(V, -1)
	{
		// pii(最短距離, 頂点の番号)
		priority_queue<pii, vector<pii>, greater<pii> > pq;

		d[s] = 0;
		pq.push(pii(0, s));

		while (!pq.empty()) {
			pii p = pq.top(); pq.pop();
			// まだ使われていない頂点のうち距離が最小のもの
			int v = p.second;
			if (d[v] < p.first) continue;
			for (int i = 0; i < G[v].size(); i++) {
				edge e = G[v][i];
				if (d[e.to] > d[v] + e.cost) {
					d[e.to] = d[v] + e.cost;
					prev[e.to] = v;
					pq.push(pii(d[e.to], e.to));
				}
			}
		}
	}

	vector<int> shortest_path_cost() { return d; }
	int shortest_path_cost(int v) { return d[v]; }

	vector<int> get_path(int t) {
		vector<int> path;
		// t が s になるまで prev[t] を辿っていく
		for (; t != -1; t = prev[t]) path.push_back(t);
		reverse(all(path));
		return path;
	}

};


int di[] = { 0, 1 };
int dj[] = { 1, 0 };

vector<vector<edge>> G;

int main() {

	//clock_t start, end;
	//start = clock();

	int H, W;
	cin >> H >> W;
	vector<string> S(H);
	cin >> S;

	int numBlack = 0;
	for (int i = 0; i < H; i++) {
		for (int j = 0; j < W; j++) {
			if (S[i][j] == '#') numBlack++;
		}
	}

	G.resize(H * W);

	for (int i = 0; i < H - 1; i++) {
		for (int j = 0; j < W - 1; j++) {
			int k = i * W + j;
			if (S[i][j] == '#') continue;

			for (int d = 0; d < 2; d++) {
				int ni = i + di[d];
				int nj = j + dj[d];
				if (ni < 0 || H <= ni || nj < 0 || W <= nj || S[ni][nj] == '#') continue;
				int nk = ni * W + nj;
				G[k].push_back(edge(-1, nk, 1)); G[nk].push_back(edge(-1, k, 1));
			}
		}
	}

	for (int i = 0; i < H - 1; i++) {
		int j = W - 1;
		int k = i * W + j;
		if (S[i][j] == '#') continue;

		int ni = i + 1;
		int nj = j;

		if (ni < 0 || H <= ni || nj < 0 || W <= nj || S[ni][nj] == '#') continue;
		int nk = ni * W + nj;
		G[k].push_back(edge(-1, nk, 1)); G[nk].push_back(edge(-1, k, 1));
	}

	for (int j = 0; j < W - 1; j++) {
		int i = H - 1;
		int k = i * W + j;
		if (S[i][j] == '#') continue;

		int ni = i;
		int nj = j + 1;

		if (ni < 0 || H <= ni || nj < 0 || W <= nj || S[ni][nj] == '#') continue;
		int nk = ni * W + nj;
		G[k].push_back(edge(-1, nk, 1)); G[nk].push_back(edge(-1, k, 1));
	}

	Dijkstra dijkstra(G, G.size(), 0);
	
	int path = dijkstra.shortest_path_cost(H * W - 1);
	path++;

	if (path > 100000) {
		cout << -1 << endl;
		return 0;
	}
	
	cout << H * W - path - numBlack << endl;

	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}




Measured memory_bytes: 512