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:
N,M = map(int,input().split(' '))

tree_list = [[] for _ in range(N) ]
LRC = sorted([list(map(int, input().split())) for i in range(M)], key=lambda x: (x[0], x[1]))
inf = float('inf')
dp = [inf] * N
dp[0] = 0
flag = False
if LRC[0][0] != 1:
    print(-1) 
else:
    for l, r, c in LRC:
        l = l -1
        r = r -1
        '''
        if dp[l] == 1000000000000:
            flag = True
            break
        '''
        if dp[r] > dp[l] + c:
            for i in reversed(range(l+1,r+1)):
                if dp[i] > dp[l] + c:
                    dp[i] = dp[l] + c
                else:
                    break 
    if dp[N-1] < inf:
        print(dp[N-1])
    else:
        print(-1)