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:
INF = 10 ** 15
MOD = 10 ** 9 + 7 
from heapq import heappop,heappush,heapify
def dijkstra(G,start = 0):
    N = len(G)
    dist = [INF] *N
    dist[start] = 0
    q = [(0,start)]

    while q:
        d,v = heappop(q)
        if d > dist[v]:
            continue
        for e,c in G[v]:
            if dist[v] + c < dist[e]:
                dist[e] = dist[v] + c
                heappush(q,(dist[e],e))
    return dist[-1]

def main():
    N,M = map(int,input().split())
    G = [[] for _ in range(N)]
    for _ in range(M):
        l,r,c = map(int,input().split())
        l -= 1
        r -= 1
        G[l].append((r,c))
        G[r].append((l,c))
    for i in range(N - 1):
        G[i + 1].append((i,0))
    ans = dijkstra(G)
    print(ans if ans < INF else -1)
if __name__ == '__main__':
    main()