#include <bits/stdc++.h>

using namespace std;

const int INF = 1 << 30;

vector<int> dx = {-1, -1, -1, 0, 0, 1, 1, 1};
vector<int> dy = {-1, 0, 1, -1, 1, -1, 0, 1};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int h, w; cin >> h >> w;
    vector<vector<int>> a(h, vector<int>(w));
    for(int i = 1; i < h - 1; i++){
        for(int j = 0; j < w; j++){
            cin >> a[i][j];
        }
    }
    vector<vector<int>> res(h, vector<int>(w, INF));
    using T = tuple<int, int, int>;
    priority_queue<T, vector<T>, greater<T>> q;
    for(int i = 1; i < h - 1; i++){
        if(a[i][0] != -1){
            q.emplace(a[i][0], i, 0);
            res[i][0] = a[i][0];
        }
    }
    while(q.size()){
        auto [cost, x, y] = q.top();
        q.pop();
        if(cost > res[x][y]){
            continue;
        }
        for(int i = 0; i < 8; i++){
            int x2 = x + dx[i], y2 = y + dy[i];
            if(1 <= x2 && x2 < h - 1 && 0 <= y2 && y2 < w){
                if(a[x2][y2] == -1) continue;
                if(res[x2][y2] > cost + a[x2][y2]){
                    res[x2][y2] = cost + a[x2][y2];
                    q.emplace(res[x2][y2], x2, y2);
                }
            }
        }
    }
    int ans = INF;
    for(int i = 1; i < h - 1; i++){
        ans = min(ans, res[i][w - 1]);
    }
    if(ans == INF){
        cout << -1 << endl;
    }else{
        cout << ans << endl;
    }
}