## https://yukicoder.me/problems/no/1283

import heapq

MAX_INT = 10 ** 18

def main():
    N, M = map(int, input().split())
    pass_map = [[0] * N for _ in range(N)]
    for _ in range(M):
        h, w, c = map(int, input().split())
        pass_map[h - 1][w - 1] = c
    
    seen = [[[MAX_INT] * N for _ in range(N)] for _ in range(2)]
    seen[0][0][0] = 0
    fix = [[[MAX_INT] * N for _ in range(N)] for _ in range(2)]
    queue = []
    heapq.heappush(queue, (0, 0, 0, 0))
    while len(queue) > 0:
        cost, state, h, w = heapq.heappop(queue) 
        if fix[state][h][w] <= cost:
            continue

        fix[state][h][w] = cost
        for dh, dw in ((0, 1), (1, 0), (0, -1), (-1, 0)):
            new_h = h + dh
            new_w = w + dw
            if 0 <= new_h and new_h < N and 0 <= new_w and new_w < N:
                # 普通に手数料を払う場合
                if fix[state][new_h][new_w] >= MAX_INT:
                    new_cost = cost + 1 + pass_map[new_h][new_w]
                    if seen[state][new_h][new_w] > new_cost:
                        seen[state][new_h][new_w] = new_cost
                        heapq.heappush(queue, (new_cost, state, new_h, new_w))
                
                # 免除を使う場合
                if state == 0 and pass_map[new_h][new_w] > 0:
                    if fix[1][new_h][new_w] >= MAX_INT:
                        new_cost = cost + 1
                        if seen[1][new_h][new_w] > new_cost:
                            seen[1][new_h][new_w] = new_cost
                            heapq.heappush(queue, (new_cost, 1, new_h, new_w))
    
    answer = min(fix[0][N - 1][N - 1], fix[1][N - 1][N - 1])
    if answer == float("inf"):
        print(-1)
    else:
        print(answer)









if __name__ == "__main__":
    main()