import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int h = sc.nextInt();
        int w = sc.nextInt();
        int[][] field = new int[h][w];
        for (int i = 1; i < h - 1; i++) {
            for (int j = 0; j < w; j++) {
                field[i][j] = sc.nextInt();
                if (field[i][j] < 0) {
                    field[i][j] = 1000000;
                }
            }
        }
        Arrays.fill(field[0], 1000000);
        Arrays.fill(field[h - 1], 1000000);
        int[][] dp = new int[h][w];
        Arrays.fill(dp[0], 1000000);
        Arrays.fill(dp[h - 1], 1000000);
        for (int i = 0; i < h; i++) {
            dp[i][0] = field[i][0];
        }
        for (int i = 1; i < w; i++) {
            for (int j = 1; j < h - 1; j++) {
                dp[j][i] = Math.min(Math.min(dp[j - 1][i - 1], dp[j + 1][i - 1]), dp[j][i - 1]) + field[j][i];
            }
        }
        int ans = 1000000;
        for (int i = 1; i < h - 1; i++) {
            ans = Math.min(ans, dp[i][w - 1]);
        }
        if (ans >= 1000000) {
            System.out.println(-1);
        } else {
            System.out.println(ans);
        }
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}