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 sys
from heapq import heappop as hpp, heappush as hp
inf = 10**20
def dijkstra(N, s, Edge):
    dist = [inf] * N
    Q = [(0, s)]
    decided = set()
    for _ in range(N):
        while True:
            dn, vn = hpp(Q)
            if vn not in decided:
                decided.add(vn)
                dist[vn] = dn
                break
        for vf, df in Edge[vn]:
            if vf not in decided:
                hp(Q, (dn + df, vf))
    return dist

readline = sys.stdin.readline
N, M = map(int, readline().split())

Edge = [[] for _ in range(N)]
for i in range(M):
    L, R, C = map(int, readline().split())
    L -= 1
    R -= 1
    Edge[L].append((R, C))

for i in range(1, N):
    Edge[i].append((i-1, 0))
for i in range(1, N):
    Edge[0].append((i, inf))
dist = dijkstra(N, 0, Edge)
if dist[N-1] == inf:
    ans = -1
else:
    ans = dist[N-1]
print(ans)