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
import os
import sys

if os.getenv("LOCAL"):
    sys.stdin = open("_in.txt", "r")

sys.setrecursionlimit(10 ** 9)
INF = float("inf")
IINF = 10 ** 18
MOD = 10 ** 9 + 7
# MOD = 998244353

N, M = list(map(int, sys.stdin.readline().split()))
LRC = [list(map(int, sys.stdin.readline().split())) for _ in range(M)]


def test():
    LRC.sort()
    dp = [INF] * N
    dp[0] = 0
    for l, r, c in LRC:
        l -= 1
        r -= 1
        for i in range(l, r + 1):
            dp[i] = min(dp[i], dp[l] + c)
    if dp[-1] == INF:
        print(-1)
    else:
        print(dp[-1])


# test()

heap = []
LRC.sort()
LRC = [(l - 1, r - 1, c) for l, r, c in LRC]
mi = 0
dp = [INF] * N
dp[0] = 0
for pos in range(N):
    if dp[pos] == INF:
        break
    while mi < M and LRC[mi][0] <= pos:
        l, r, c = LRC[mi]
        heapq.heappush(heap, (dp[pos] + c, r))
        mi += 1
    while heap and heap[0][1] <= pos:
        heapq.heappop(heap)
    if not heap:
        break
    dp[pos + 1] = heap[0][0]


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