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 heapq


def dijkstra(g: list, start, goal=None):
    num = len(g)          # グラフのノード数
    dist = [float('inf') for i in range(num)]

    dist[start] = 0
    # プライオリティキュー．各要素は，(startからある頂点vまでの仮の距離, 頂点vのID)からなるタプル
    q = []
    heapq.heappush(q, (0, start))  # 始点をpush

    while q:
        prov_cost, src = heapq.heappop(q)  # pop
        # プライオリティキューに格納されている最短距離が，現在計算できている最短距離より大きければ，distの更新をする必要はない
        if dist[src] < prov_cost:
            continue
        # 他の頂点の探索
        for node, cost in g[src]:
            if dist[node] > dist[src] + cost:
                dist[node] = dist[src] + cost
                heapq.heappush(q, (dist[node], node))
    return dist


n, m = map(int, input().split())
g = [[] for _ in range(n)]
for i in range(n - 1):
    g[i + 1].append((i, 0))
for i in range(m):
    l, r, c = map(int, input().split())
    g[l - 1].append((r - 1, c))
d = dijkstra(g, 0)
if d[n - 1] == float('inf'):
    print(-1)
else:
    print(d[n - 1])