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 heappush, heappop
import sys
input = sys.stdin.readline

INF = float('inf')

# 単一始点最短経路を求める（Dijkstra法）
def Dijkstra(adjList, vSt):
    numV = len(adjList)
    numUsed = 0
    costs = [INF] * numV
    costs[vSt] = 0
    PQ = []
    heappush(PQ, (0, vSt))
    while PQ:
        cNow, vNow = heappop(PQ)
        if cNow > costs[vNow]: continue
        numUsed += 1
        if numUsed == numV: break
        for v2, wt in adjList[vNow]:
            c2 = cNow + wt
            if c2 < costs[v2]:
                costs[v2] = c2
                heappush(PQ, (c2, v2))
    return costs

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

for i in range(N-1):
    adjL[i+1].append((i, 0))

costs = Dijkstra(adjL, 0)

if costs[-1] == INF:
    print(-1)
else:
    print(costs[-1])