#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;

typedef modint998244353 mint;
typedef long long ll;

int main(){
	int h, w; cin >> h >> w;
	vector<vector<int>> a(h-2, vector<int>(w));
	for (int i=0; i<h-2; i++){
		for (int j=0; j<w; j++){
			cin >> a[i][j];
		}
	}
	vector<vector<vector<pair<int,int>>>> ikeru(h-2, vector<vector<pair<int,int>>>(w, vector<pair<int,int>>(0)));
	vector<pair<int,int>> go = {
		pair(0,-1), pair(0,1),
		pair(-1,-1), pair(-1,0), pair(-1,1),
		pair(1,-1), pair(1,0), pair(1,1)
	};
	for (int i=0; i<h-2; i++){
		for (int j=0; j<w; j++){
			for (auto[xx,yy]:go){
				int x = i+xx;
				int y = j+yy;
				if (0<=x && x<h-2 && 0<=y && y<w && a[x][y] != -1){
					ikeru[i][j].push_back(pair(x,y));
				}
			}
		}
	}
	vector<vector<int>> d(h-2, vector<int>(w, 1e9));
	priority_queue<tuple<int,int,int>> pq;
	for (int i=0; i<h-2; i++){
		if (a[i][0] != -1){
			pq.push(make_tuple(-a[i][0], i, 0));
			d[i][0] = a[i][0];
		}
	}
	while(!pq.empty()){
		int t = -get<0>(pq.top());
		int i = get<1>(pq.top());
		int j = get<2>(pq.top());
		pq.pop();
		if (t > d[i][j]) continue;
		for (auto [x, y]: ikeru[i][j]){
			if (t + a[x][y] < d[x][y]){
				d[x][y] = t + a[x][y];
				pq.push(make_tuple(-d[x][y], x, y));
			}
		}
	}
	
	int ans = 1e9;
	for (int i=0; i<h-2; i++){
		ans = min(ans, d[i][w-1]);
	}
	if (ans == 1e9) cout << -1 << endl;
	else cout << ans << endl;
}