#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
#define drep(i, cc, n) for (ll i = (cc); i <= (n); ++i)
#define rep(i, n) drep(i, 0, n - 1)
#define all(a) (a).begin(), (a).end()
#define pb push_back
#define fi first
#define se second

mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
const ll MOD1000000007 = 1000000007;
const ll MOD998244353 = 998244353;
const ll MOD[3] = {999727999, 1070777777, 1000000007};
const ll LINF = 1LL << 60;
const int IINF = 1 << 30 - 1;

template<typename T> struct Edge{
    int to; T w;
    Edge(int to_, T w_=1){
        to = to_;
        w=w_;
    }
};
template<typename T> using Tree = vector<vector<Edge<T>>>;
template<typename T> using Graph = vector<vector<Edge<T>>>;
/* 容量&重み付きエッジ for Dinic */
template<typename T> struct REdge{
    int to;
    T cap;
    T cost;
    int rev;
    REdge(int to_, T cap_, T cost_=1){
        to = to_;
        cap = cap_;
        cost = cost_;
    }
    
    REdge(int to_, T cap_, T cost_, int rev_){
        to = to_;
        cap = cap_;
        cost = cost_;
        rev = rev_;
    }
};

/* 残余グラフ for Dinic */
template<typename T> using RGraph = vector<vector<REdge<T>>>;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    
    ll h, w; cin >> h >> w;
    vector<vector<ll>> a(h, vector<ll>(w));
    for(ll i=1; i<h-1; i++) for(ll j=0; j<w; j++) cin >> a[i][j];

    ll di[5] = {-1, -1, 0, 1, 1};
    ll dj[5] = {0, 1, 1, 1, 0};
    ll ans = LINF;
    vector<vector<ll>> cost(h, vector<ll>(w, LINF));
    priority_queue<tuple<ll, ll, ll>, vector<tuple<ll, ll, ll>>, greater<tuple<ll, ll, ll>>> PQ;
    for(ll si=1; si<h-1; si++){
        if(a[si][0]==-1) continue;
        //start地点 : (si, 0)
        cost[si][0] = a[si][0];
        PQ.push({cost[si][0], si, 0});
    }

    while(!PQ.empty()){
        ll tmp_cost = get<0>(PQ.top());
        ll now_i = get<1>(PQ.top());
        ll now_j = get<2>(PQ.top());
        PQ.pop();
        if(cost[now_i][now_j] < tmp_cost) continue;

        rep(k, 5){
            ll next_i = now_i + di[k];
            ll next_j = now_j + dj[k];
            if(next_i <= 0 || next_j < 0 || h-1<=next_i || w<=next_j) continue;
            if(a[next_i][next_j]==-1) continue;
            if(cost[now_i][now_j]+a[next_i][next_j]<cost[next_i][next_j]){
                cost[next_i][next_j] = cost[now_i][now_j]+a[next_i][next_j];
                PQ.push({cost[next_i][next_j], next_i, next_j});
            }
        }
    }

    for(ll i=1; i<=h-1; i++) ans = min(ans, cost[i][w-1]);

    if(ans==LINF) cout << -1 << endl;
    else cout << ans << endl;
}