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
from collections import defaultdict

INF = float('inf')
def dijkstra(V, E, s):
    '''
    Input:
        V = list(range(N))
        E = defaultdict(dict)
        s (in V) : start vertex
    Output:
        dist: the list of the minimum cost from s to arbitrary vertex v in the given graph
    '''
    dist = {v: INF for v in V}
    heap = []
    dist[s] = 0; rem = len(V);
    heappush(heap, (0, s))
    while heap and rem:
        d, v = heappop(heap)
        # don't need to check when the stored value is greater than provisional distance
        if d > dist[v]: continue
        rem -= 1;
        for u, c in E[v].items():
            temp = d + c
            if temp < dist[u]:
                dist[u] = temp
                heappush(heap, (temp, u))
    return dist

N, M = map(int, input().split())
V = list(range(N))
E = defaultdict(dict)
for i in range(N):
    E[i+1][i] = 0
for _ in range(M):
    l, r, c = map(int, input().split())
    l, r = l-1, r-1
    E[l][r] = min(c, E[l].setdefault(r, INF))
dist = dijkstra(V, E, 0)
print(dist[N-1] if dist[N-1] != INF else -1)