import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.util.PriorityQueue;

public class Main {
    static PrintWriter out;
    static InputReader ir;
    static final int[] dx = { 0, 1, 0, -1 };
    static final int[] dy = { 1, 0, -1, 0 };

    static void solve() {
        int n = ir.nextInt();
        int m = ir.nextInt();
        HashMap<Long, Long> mp = new HashMap<>();
        for (int i = 0; i < m; i++) {
            int h = ir.nextInt() - 1;
            int w = ir.nextInt() - 1;
            long c = ir.nextLong();
            mp.put((long) h << 10 | w, c);
        }
        Graph[] g = new Graph[n * n * 2];
        for (int i = 0; i < n * n * 2; i++)
            g[i] = new Graph();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                for (int k = 0; k < 4; k++) {
                    int nx = i + dx[k];
                    int ny = j + dy[k];
                    if (nx < 0 || ny < 0 || nx >= n || ny >= n)
                        continue;
                    long cost = 1;
                    if (mp.containsKey((long) nx << 10 | ny)) {
                        cost += mp.get((long) nx << 10 | ny);
                    }
                    g[i * n + j].add(new long[] { nx * n + ny, cost });
                    g[n * n + i * n + j].add(new long[] { n * n + nx * n + ny, cost });
                    if (cost > 1) {
                        g[i * n + j].add(new long[] { n * n + nx * n + ny, 1 });
                    }
                }
            }
        }
        long[] d = dijkstra(0, g);
        out.println(Math.min(d[n * n - 1], d[n * n * 2 - 1]));
    }

    public static long[] dijkstra(int s, Graph[] g) {
        long[] d = new long[g.length];
        PriorityQueue<long[]> pq = new PriorityQueue<long[]>(new Comparator<long[]>() {
            public int compare(long[] a, long[] b) {
                return Long.compare(a[1], b[1]);
            }
        });
        Arrays.fill(d, 1L << 60);
        d[s] = 0;
        pq.offer(new long[] { s, 0 });
        while (!pq.isEmpty()) {
            long[] p = pq.poll();
            int from = (int) p[0];
            if (d[from] != p[1])
                continue;
            for (int i = 0; i < g[from].size(); i++) {
                long[] e = g[from].get(i);
                int to = (int) e[0];
                if (d[to] > d[from] + e[1]) {
                    d[to] = d[from] + e[1];
                    pq.offer(new long[] { to, d[to] });
                }
            }
        }
        return d;
    }

    static class Graph extends ArrayList<long[]> {
    }

    public static void main(String[] args) {
        ir = new InputReader(System.in);
        out = new PrintWriter(System.out);
        solve();
        out.flush();
    }

    static class InputReader {

        private InputStream in;
        private byte[] buffer = new byte[1024];
        private int curbuf;
        private int lenbuf;

        public InputReader(InputStream in) {
            this.in = in;
            this.curbuf = this.lenbuf = 0;
        }

        public boolean hasNextByte() {
            if (curbuf >= lenbuf) {
                curbuf = 0;
                try {
                    lenbuf = in.read(buffer);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (lenbuf <= 0)
                    return false;
            }
            return true;
        }

        private int readByte() {
            if (hasNextByte())
                return buffer[curbuf++];
            else
                return -1;
        }

        private boolean isSpaceChar(int c) {
            return !(c >= 33 && c <= 126);
        }

        private void skip() {
            while (hasNextByte() && isSpaceChar(buffer[curbuf]))
                curbuf++;
        }

        public boolean hasNext() {
            skip();
            return hasNextByte();
        }

        public String next() {
            if (!hasNext())
                throw new NoSuchElementException();
            StringBuilder sb = new StringBuilder();
            int b = readByte();
            while (!isSpaceChar(b)) {
                sb.appendCodePoint(b);
                b = readByte();
            }
            return sb.toString();
        }

        public int nextInt() {
            if (!hasNext())
                throw new NoSuchElementException();
            int c = readByte();
            while (isSpaceChar(c))
                c = readByte();
            boolean minus = false;
            if (c == '-') {
                minus = true;
                c = readByte();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res = res * 10 + c - '0';
                c = readByte();
            } while (!isSpaceChar(c));
            return (minus) ? -res : res;
        }

        public long nextLong() {
            if (!hasNext())
                throw new NoSuchElementException();
            int c = readByte();
            while (isSpaceChar(c))
                c = readByte();
            boolean minus = false;
            if (c == '-') {
                minus = true;
                c = readByte();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res = res * 10 + c - '0';
                c = readByte();
            } while (!isSpaceChar(c));
            return (minus) ? -res : res;
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[][] nextCharMap(int n, int m) {
            char[][] map = new char[n][m];
            for (int i = 0; i < n; i++)
                map[i] = next().toCharArray();
            return map;
        }
    }

    static void tr(Object... o) {
        System.err.println(Arrays.deepToString(o));
    }
}