#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <stack>
#include <math.h>
#include <cassert>
#include <bitset>
#include <map>
#include <algorithm>
#include <iterator>
#include <string>
#include <utility>
#include <numeric>
#include <regex>
#include <complex>
#include <random>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>
ostream &operator<<(ostream &os,const pair<T1,T2>&p){
  os<<p.first<<" "<<p.second;
  return os;
}
template<typename T1,typename T2>
istream &operator>>(istream &is,pair<T1,T2>&p){
  is>>p.first>>p.second;
  return is;
}
template<typename T>
istream &operator>>(istream &is,vector<T> &a){
  for(auto &i:a)is>>i;
  return is;
}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
ll myceil(ll a,ll b){return (a+b-1)/b;}
int h,w;
bool inarea(int x,int y){
  if(x<0)return false;
  if(y<0)return false;
  if(x>h-1)return false;
  if(y>w-1)return false;
  return true;
}
int main(){
  cin>>h>>w;
  h-=2;
  vector<vector<int>>a(h,vector<int>(w));
  cin>>a;
  vector<vector<int>>dst(h,vector<int>(w,1e9));
  minque<pair<int,pair<int,int>>>que;
  rep(i,h){
    if(a[i][0]!=-1){
      dst[i][0]=a[i][0];
      que.push({a[i][0],{i,0}});
    }
  }
  while(!que.empty()){
    auto [d,p]=que.top();
    que.pop();
    int x,y;
    tie(x,y)=p;
    if(dst[x][y]!=d)continue;
    reps(dx,-1,2)reps(dy,-1,2){
      if(dx==0&&dy==0)continue;
      int cx=x+dx,cy=y+dy;
      if(inarea(cx,cy)){
        if(a[cx][cy]!=-1&&chmin(dst[cx][cy],dst[x][y]+a[cx][cy]))que.push({dst[cx][cy],{cx,cy}});
      }
    }
  }
  int ans=1e9;
  rep(i,h)chmin(ans,dst[i][w-1]);
  if(ans==1e9)cout<<-1<<endl;
  else cout<<ans<<endl;
}