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
input = sys.stdin.readline
n, m = map(int,input().split())
C = [list(map(int,input().split())) for i in range(m)]
S = [0] * n

for i in range(m):
    for j in range(2):
        C[i][j] -= 1

for i in range(m):
    S[C[i][0]] += 1
    S[C[i][1]] -= 1

for i in range(1, n):
    S[i] += S[i-1]

for i in range(n-1):
    if S[i] > 0:
        C.append([i+1, i, 0])

M = [[] for i in range(n)]
for i in range(len(C)):
    M[C[i][0]].append([C[i][1], C[i][2]])
    if C[i][2] > 0:
        M[C[i][1]].append([C[i][0], C[i][2]])

import heapq

D = [float("inf")] * n
P = [-1] * n
D[0] = 0
V = [0] * n
Q = []
for v in range(n):
    heapq.heappush(Q, [D[v], v])

le = len(Q)
while le > 0:
    q = heapq.heappop(Q)
    u = q[1]
    du = q[0]
    if V[u] == 0:
        V[u] = 1
        le -= 1
        for i in range(len(M[u])):
            v = M[u][i][0]
            luv = M[u][i][1]
            if V[v] == 0:
                alt = du + luv
                if D[v] > alt:
                    D[v] = alt
                    P[v] = u
                    heapq.heappush(Q, [alt, v])

ans = D[-1]
if ans == float("inf"):
    ans = -1
print(ans)