INF = 1e18
from heapq import heappop, heappush
def main():
    N, M = map(int, input().split())
    def check(i, j):
        return 0 <= i < N and 0 <= j < N

    memo = [[0] * (N) for _ in range(N)]
    for i in range(M):
        h, w, c = map(int, input().split())
        h -= 1
        w -= 1
        memo[h][w] = c

    kakutei = [[[False] * (2) for _ in range(N)] for _ in range(N)]
    cost = [[[INF] * (2) for _ in range(N)] for _ in range(N)]
    cost[0][0][0] = 0
    que = []
    heappush(que, (0, 0, 0, 0)) # cost_cur, i, j, k
    while que:
        curr_cost, i, j, k = heappop(que)
        if kakutei[i][j][k]:
            continue
        kakutei[i][j][k] = True
        for ii, jj in [(0, -1), (0, 1), (-1, 0), (1, 0)]:
            ni, nj = i+ii, j+jj
            if not check(ni, nj):
                continue
            # 同じ高さ
            if cost[ni][nj][k] > curr_cost + memo[ni][nj] + 1:
                cost[ni][nj][k] = curr_cost + memo[ni][nj] + 1
                heappush(que, (cost[ni][nj][k], ni, nj, k))
            if k == 0 and cost[ni][nj][1] > curr_cost + 1:
                cost[ni][nj][1] = curr_cost + 1
                heappush(que, (cost[ni][nj][1], ni, nj, 1))
    print(min(cost[-1][-1]))
if __name__ == "__main__":
    main()