Problem: We have N points numbered 1 to N arranged in a line in this order.

Takahashi decides to make an undirected graph, using these points as the vertices. In the beginning, the graph has no edge. Takahashi will do M operations to add edges in this graph. The i-th operation is as follows:

* The operation uses integers L_i and R_i between 1 and N (inclusive), and a positive integer C_i. For every pair of integers (s, t) such that L_i \leq s < t \leq R_i, add an edge of length C_i between Vertex s and Vertex t.



The integers L_1, ..., L_M, R_1, ..., R_M, C_1, ..., C_M are all given as input.

Takahashi wants to solve the shortest path problem in the final graph obtained. Find the length of the shortest path from Vertex 1 to Vertex N in the final graph.

Constraints

* 2 \leq N \leq 10^5
* 1 \leq M \leq 10^5
* 1 \leq L_i < R_i \leq N
* 1 \leq C_i \leq 10^9

Input

Input is given from Standard Input in the following format:


N M
L_1 R_1 C_1
:
L_M R_M C_M


Output

Print the length of the shortest path from Vertex 1 to Vertex N in the final graph. If there is no shortest path, print `-1` instead.

Examples

Input

4 3
1 3 2
2 4 3
1 4 6


Output

5


Input

4 2
1 2 1
3 4 2


Output

-1


Input

10 7
1 5 18
3 4 8
1 3 5
4 7 10
5 9 8
6 10 5
8 10 3


Output

28

Solution (in PYTHON3):

Solution:
import sys
import heapq
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

INF = 10**30
N, M = map(int, input().split())
G = [[]for i in range(N)]
for i in range(1, N):
    G[i].append([i-1, 0])

for i in range(M):
    L, R, C = map(int, input().split())
    G[L-1].append([R-1, C])

S = 0

def dijkstra(N, S):
    d = [INF for i in range(N)]

    que = []
    d[S] = 0
    heapq.heappush(que, [0, S])

    while not(len(que) == 0):
        q = heapq.heappop(que)
        ver = q[1] # ノード
        dis = q[0] # 過去に更新された最短距離

        # vまで2番目に短い距離（最新）　＜　過去最短距離　の時、
        # キューから取り出した過去のものを無視する
        if d[ver] < dis:
            continue

        # 隣接リストに対してループ
        for i in range(len(G[ver])):
            e = G[ver][i]
            if d[e[0]] > d[ver] + e[1]:
                d[e[0]] = d[ver] + e[1]
                heapq.heappush(que, [d[e[0]], e[0]])

    return d[N-1]

ans = dijkstra(N, S)
if ans == INF:
    print(-1)
else:
    print(ans)