// 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));
  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];
    }
  }
  for (int j=1;j<w;j++) {
    priority_queue<P, vector<P>, greater<P>> que;
    for (int i=1;i<h-1;i++) {
      if (a[i][j] == -1) continue;
      dp[i][j] = a[i][j] + min(dp[i-1][j-1], min(dp[i][j-1], dp[i+1][j-1]));
      que.push(P(dp[i][j], i));
    }
    while(!que.empty()) {
      auto [v, i] = que.top(); que.pop();
      if (dp[i][j] < v) continue;
      if (i-1>=0 && a[i-1][j] != -1) {
        int nv = v + a[i-1][j];
        if (dp[i-1][j] > nv) {
          que.push(P(nv, i-1));
          dp[i-1][j] = nv;
        }
      }
      if (i+1<h-1 && a[i+1][j] != -1) {
        int nv = v + a[i+1][j];
        if (dp[i+1][j] > nv) {
          que.push(P(nv, i+1));
          dp[i+1][j] = 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;
}