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:
from heapq import heappop, heappush, heapify

class Graph():  #directed
    def __init__(self, n, edge, indexed=1):
        self.n = n
        self.graph = [[] for _ in range(n)]
        self.deg = [0 for _ in range(n)]
        for e in edge:
            self.graph[e[0] - indexed].append((e[1] - indexed, e[2]))
            self.deg[e[1] - indexed] += 1

    def dijkstra(self, s, INF=10**18, restore_to=None):
        dist = [INF for _ in range(self.n)]
        dist[s] = 0
        heap = [(0, s)]
        while heap:
            cost, node = heappop(heap)
            if dist[node] < cost:
                continue
            for adj, adjcost in self.graph[node]:
                if dist[node] + adjcost < dist[adj]:
                    dist[adj] = dist[node] + adjcost
                    heappush(heap, (dist[adj], adj))
        if restore_to is not None:
            g = restore_to
            if dist[g] == INF:
                return dist, False
            path = [g]
            node = g
            while node != s:
                node = prev[node]
                path.append(node)
            return dist, path[::-1]
        return dist

import sys
input = sys.stdin.readline

N, M = map(int, input().split())
E = list()

for _ in range(M):
    l, r, c = map(int, input().split())
    E.append((l - 1, r - 1, c))

for i in range(N - 1):
    E.append((i + 1, i, 0))

g = Graph(N, E, 0)
res = g.dijkstra(0)[N - 1]

print(res if res != 10**18 else -1)