typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long

signed main(){
    ll h,w;
    std::cin >> h>>w;
    h-=2;
    vector<vector<ll>> a(h,vector<ll>(w));
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            std::cin >> a[i][j];
        }
    }
    vector<vector<ll>> dis(h,vector<ll>(w,1e18));
    using P = pair<ll,pair<ll,ll>>;
    priority_queue<P,vector<P>,greater<P>> pq;
    for (int i = 0; i < h; i++) {
        if(a[i][0]==-1)continue;
        dis[i][0] = a[i][0];
        pq.push({dis[i][0], {i,0}});
    }

    while(!pq.empty()){
        auto [d, p] = pq.top();pq.pop();
        auto [i,j] = p;
        
        if(dis[i][j]<d)continue;
        
        for (int x = -1; x <= 1; x++) {
            for (int y = -1; y <= 1; y++) {
                if(i+x<0||i+x>=h||j+y<0||j+y>=w)continue;
                if(a[i+x][j+y]==-1)continue;
                 if(dis[i+x][j+y]>d+a[i+x][j+y]){
                     dis[i+x][j+y] = d+a[i+x][j+y];
                     pq.push({dis[i+x][j+y], {i+x, j+y}});
                 }
            }
        }
    }
    
    ll ans = 1e18;
    
    for (int i = 0; i < h; i++) {
        ans = min(ans, dis[i][w-1]);
    }
    if(ans==1e18){
        std::cout << -1 << std::endl;
    }else{
        std::cout << ans << std::endl;
    }
}