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

import heapq

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 = [[[float("inf"), float("inf")] for _ in range(N)] for _ in range(N)]
    seen[0][0][0] = 0
    fix = [[[float("inf"), float("inf")] for _ in range(N)] for _ in range(N)]
    queue = []
    heapq.heappush(queue, (0, 0, 0, 0))
    while len(queue) > 0:
        cost, h, w, state = heapq.heappop(queue) 
        if fix[h][w][state] <= cost:
            continue

        fix[h][w][state] = 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[new_h][new_w][state] != float("inf"):
                    continue

                new_cost = cost + 1 + pass_map[new_h][new_w]
                if seen[new_h][new_w][state] > new_cost:
                    seen[new_h][new_w][state] = new_cost
                    heapq.heappush(queue, (new_cost, new_h, new_w, state))
                
                # 免除を使う場合
                if state == 0 and pass_map[new_h][new_w] > 0:
                    if fix[new_h][new_w][1] != float("inf"):
                        continue

                    new_cost = cost + 1
                    if seen[new_h][new_w][1] > new_cost:
                        seen[new_h][new_w][1] = new_cost
                        heapq.heappush(queue, (new_cost, new_h, new_w, 1))
    
    answer = min(fix[N - 1][N - 1])
    if answer == float("inf"):
        print(-1)
    else:
        print(answer)









if __name__ == "__main__":
    main()