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:
"""
#editorialより
頂点1から頂点iへの最短路の長さをdiとするとd1≦d2≦....≦dN
各iに対して頂点i+ 1から頂点iに長さ0の辺を追加
このときi回目に追加される辺について考えると、
頂点Liから頂点Riへの長さCiの辺を追加すれば十分
"""
import sys,heapq
input = sys.stdin.readline

n,m = map(int,input().split( ))
Ad = [[] for _ in range(n)]
for i in range(m):
    li,ri,ci = map(int, input().split( ))
    Ad[li-1].append((ri-1,ci))
for i in range(1,n):
    Ad[i].append((i-1,0))

inf = 10**20###これ不十分だった
D = [inf for _ in range(n)]
#Prev = [-1 for _ in range(n)]
D[0] = 0
Q = []
heapq.heappush(Q, (0,0))

while Q:
    d,q = heapq.heappop(Q) #qは[距離、頂点番号]：キューの優先度の都合で番号が後
    #print(q)
    for v,c in Ad[q]:
        if D[v]>d+c:
            D[v] = d+c
            #Prev[n[0]] = q[1]
            heapq.heappush(Q, (d+c,v))

if D[n-1]<inf:
    print(D[n-1])
else:
    print(-1)