import std.conv, std.functional, std.range, std.stdio, std.string; import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons; import core.bitop; class EOFException : Throwable { this() { super("EOF"); } } string[] tokens; string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; } int readInt() { return readToken.to!int; } long readLong() { return readToken.to!long; } real readReal() { return readToken.to!real; } bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } } bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } } int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; } int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); } int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); } enum DX = [+1, 0, -1, 0]; enum DY = [0, +1, 0, -1]; enum INF = 10L^^18; void main() { try { for (; ; ) { const N = readInt(); const M = readInt(); auto H = new int[M]; auto W = new int[M]; auto C = new long[M]; foreach (i; 0 .. M) { H[i] = readInt() - 1; W[i] = readInt() - 1; C[i] = readLong(); } auto cost = new long[][](N, N); foreach (i; 0 .. M) { cost[H[i]][W[i]] += C[i]; } alias Entry = Tuple!(long, "c", int, "x", int, "y", int, "s"); BinaryHeap!(Array!Entry, "a.c > b.c") que; auto dist = new long[][][](N, N, 2); foreach (x; 0 .. N) foreach (y; 0 .. N) { dist[x][y][] = INF; } chmin(dist[0][0][0], 0); que.insert(Entry(0, 0, 0, 0)); for (; !que.empty; ) { const c = que.front.c; const x = que.front.x; const y = que.front.y; const s = que.front.s; que.removeFront; if (dist[x][y][s] == c) { foreach (dir; 0 .. 4) { const xx = x + DX[dir]; const yy = y + DY[dir]; if (0 <= xx && xx < N && 0 <= yy && yy < N) { { const cc = c + 1 + cost[xx][yy]; if (chmin(dist[xx][yy][s], cc)) { que.insert(Entry(cc, xx, yy, s)); } } if (s == 0) { const cc = c + 1; if (chmin(dist[xx][yy][1], cc)) { que.insert(Entry(cc, xx, yy, 1)); } } } } } } long ans = INF; foreach (s; 0 .. 2) { chmin(ans, dist[N - 1][N - 1][s]); } writeln(ans); } } catch (EOFException e) { } }