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
inf = float('inf')

# 計算量O((E+V)logV)
# 引数(始点,隣接リスト)
def dijkstra(start,ad):
    global dist
    #global cnt
    N = len(ad)
    dist = [inf] * N
    dist[start] = 0
    #cnt = [0] * N
    #cnt[start] = 1
    pq = [(dist[start], start)]
    while pq:
        dist_v, v = heappop(pq)
        for nv, nw in ad[v]:
            if dist[nv] > dist_v + nw:
                dist[nv] = dist_v + nw
                heappush(pq,(dist[nv], nv))
            #if dist[nv] == dist_v + nw:
                #cnt[nv] += cnt[v]
                #cnt[nv] %= mod

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

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

dijkstra(0, to)

ans = dist[N-1]
if ans == inf:
    ans = -1
print(ans)