#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int h, w;
    cin >> h >> w;
    h -= 2;
    ll INF = 1ll << 60;
    vector<vector<ll>> A(h, vector<ll>(w)), B(h, vector<ll>(w, 1ll << 60));
    for(int y = 0; y < h; y++){
        for(int x = 0; x < w; x++){
            cin >> A[y][x];
            if(A[y][x] == -1) A[y][x] = INF;
        }
    }
    priority_queue<tuple<ll, int, int>, vector<tuple<ll, int, int>>, greater<tuple<ll, int, int>>> pq;
    for(int y = 0; y < h; y++){
        pq.emplace(A[y][0], y, 0);
        B[y][0] = A[y][0];
    }
    while(!pq.empty()){
        ll d;
        int y, x;
        tie(d, y, x) = pq.top();
        pq.pop();
        if(d > B[y][x]) continue;
        for(int dy = -1; dy <= 1; dy++){
            for(int dx = -1; dx <= 1; dx++){
                if(dy == 0 && dx == 0) continue;
                int ny = y + dy, nx = x + dx;
                if(ny < 0 || ny >= h || nx < 0 || nx >= w) continue;
                ll d2 = d + A[ny][nx];
                if(d2 >= B[ny][nx]) continue;
                B[ny][nx] = d2;
                pq.emplace(d2, ny, nx);
            }
        }
    }
    ll ans = INF;
    for(int y = 0; y < h; y++){
        ans = min(ans, B[y][w - 1]);
    }
    if(ans == INF) ans = -1;
    cout << ans << '\n';
}