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 sys

input = sys.stdin.readline

def dijkstra_heap(s,N,edge):
    d = [float('inf')] * N
    used = [True] * N
    d[s] = 0
    used[s] = False
    edgelist = []
    for a, b in edge[s]:
        heapq.heappush(edgelist, a * (10 ** 6) + b)
    while len(edgelist):
        minedge = heapq.heappop(edgelist)
        if not used[minedge%(10**6)]:
            continue
        v = minedge % (10 ** 6)
        d[v] = minedge // (10 ** 6)
        used[v] = False
        for e in edge[v]:
            if used[e[1]]:
                heapq.heappush(edgelist,(e[0]+d[v])*(10**6)+e[1])
    return d


def main():
    N, M = map(int, input().split())
    edge = [[] for i in range(N)]
    for i in range(N-1):
        edge[i+1].append([0,i])
    for i in range(M):
        L, R, C = map(int, input().split())
        L -= 1
        R -= 1
        edge[L].append([C,R])
        edge[R].append([C,L])
    d = dijkstra_heap(0,N,edge)
    if d[N-1] == float('inf'):
        print(-1)
    else:
        print(d[N-1])
    

if __name__ == "__main__":
    main()