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

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] first = br.readLine().split(" ", 2);
        int n = Integer.parseInt(first[0]);
        int m = Integer.parseInt(first[1]);
        HashMap<Integer, Integer> places = new HashMap<>();
        for (int i = 0; i < m; i++) {
            String[] line = br.readLine().split(" ", 3);
            places.put((Integer.parseInt(line[0]) - 1) * n + Integer.parseInt(line[1]) - 1, Integer.parseInt(line[2]));
        }
        PriorityQueue<Path> queue = new PriorityQueue<>();
        queue.add(new Path(0, 0, 0));
        long[][] costs = new long[2][n * n];
        Arrays.fill(costs[0], Long.MAX_VALUE);
        Arrays.fill(costs[1], Long.MAX_VALUE);
        while (queue.size() > 0) {
            Path p = queue.poll();
            int add = places.getOrDefault(p.idx, 0);
            if (costs[p.level][p.idx] <= p.value + add) {
                continue;
            }
            costs[p.level][p.idx] = p.value + add;
            if (p.idx % n > 0) {
                queue.add(new Path(p.idx - 1, p.level, p.value + 1 + add));
            }
            if (p.idx % n < n - 1) {
                queue.add(new Path(p.idx + 1, p.level, p.value + 1 + add));
            }
            if (p.idx / n > 0) {
                queue.add(new Path(p.idx - n, p.level, p.value + 1 + add));
            }
            if (p.idx / n < n - 1) {
                queue.add(new Path(p.idx + n, p.level, p.value + 1 + add));
            }
            if (p.level > 0) {
                continue;
            }
            if (costs[1][p.idx] <= p.value) {
                continue;
            }
            costs[1][p.idx] = p.value;
            if (p.idx % n > 0) {
                queue.add(new Path(p.idx - 1, 1, p.value + 1));
            }
            if (p.idx % n < n - 1) {
                queue.add(new Path(p.idx + 1, 1, p.value + 1));
            }
            if (p.idx / n > 0) {
                queue.add(new Path(p.idx - n, 1, p.value + 1));
            }
            if (p.idx / n < n - 1) {
                queue.add(new Path(p.idx + n, 1, p.value + 1));
            }
        }
        System.out.println(costs[1][n * n - 1]);
    }
    
    static class Path implements Comparable<Path> {
        int idx;
        int level;
        long value;
        
        public Path(int idx, int level, long value) {
            this.idx = idx;
            this.level = level;
            this.value = value;
        }
        
        public int compareTo(Path another) {
            if (value == another.value) {
                return 0;
            } else if (value < another.value) {
                return -1;
            } else {
                return 1;
            }
        }
    }
 }