#include<bits/stdc++.h>
using namespace std;
using ll = long long;
int main(){
  // input
  int H,W; cin >> H >> W;
  H -= 2;
  vector<vector<ll>> A(W,vector<ll>(H));
  for (int i = 0; i < H; i++)
    for (int j = 0; j < W; j++)
      cin >> A[j][i];
  
  // solve: dp
  vector<vector<ll>> dp(W+1,vector<ll>(H,9e18));
  for (int j = 0; j < H; j++)
    dp[0][j] = 0;
  
  for (int i = 0; i < W; i++){
    for (int j = 0; j < H; j++){
      ll cost = A[i][j];
      if(cost == -1) continue;
      
      dp[i+1][j] = min(dp[i+1][j],dp[i][j]+cost);
      if(j - 1 >= 0)
        dp[i+1][j] = min(dp[i+1][j],dp[i][j-1]+cost);
      if(j + 1 < H)
        dp[i+1][j] = min(dp[i+1][j],dp[i][j+1]+cost);
      
      // cout << i << " " << j << " " << dp[i+1][j] << endl;
    }
  }
  
  // output
  ll ans = 9e18;
  for (int j = 0; j < H; j++)    
    ans = min(ans,dp[W][j]);
  
  cout << (ans < 9e18? ans : -1) << endl;
}