// I SELL YOU...! 
#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
#include<chrono>
#include<iomanip>
#include<map>
#include<set>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
using TP = tuple<ll,ll,ll>;
void init_io(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(18);
}
const ll INF = 1e9;
signed main(){
  init_io();
  ll h,w;
  cin >> h >> w;
  vector<vector<ll>> a(h, vector<ll>(w, -1));
  vector<vector<ll>> dp(h, vector<ll>(w, INF));
  priority_queue<TP, vector<TP>, greater<TP>> que;
  for(int i=1;i<h-1;i++){
    for(int j=0;j<w;j++) {
      cin >> a[i][j];
      if (j==0 && a[i][j] != -1) {
        dp[i][j] = a[i][j];
        que.push(TP(a[i][j], i, j));
      }
    }
  }
  while(!que.empty()) {
    auto [v, i, j] = que.top(); que.pop();
    if (dp[i][j] < v) continue;
    ll nx[] = {i-1, i+1, i-1, i, i+1};
    ll ny[] = {j, j, j+1, j+1, j+1};
    for (int t=0;t<5;t++) {
      ll ni = nx[t];
      ll nj = ny[t];
      if (ni>0 && ni <h-1 && nj < w && a[ni][nj] != -1) {
        int nv = v + a[ni][nj];
        if (dp[ni][nj] > nv) {
          que.push(TP(nv, ni, nj));
          dp[ni][nj] = nv;
        }
      }
    }
  }
  ll ans = INF;
  for (int i=0;i<h;i++) {
    ans = min(ans, dp[i][w-1]);
  }
  /*
  cout << endl;
  for (int i=0;i<h;i++) {
    for(int j=0;j<w;j++) {
      if (dp[i][j] == INF) dp[i][j] = -1;
      cout << dp[i][j] <<" ";
    }
    cout << endl;
  }
  cout << endl;
  */
  if (ans == INF) ans = -1;
  cout << ans << endl;
}