import heapq
import sys

input = sys.stdin.readline

def dijkstra_heap(s):
    #始点sから各頂点への最短距離
    d = [float("inf")] * n
    used = [True] * n #True:未確定
    d[s] = 0
    used[s] = False
    edgelist = []
    for e in edge[s]:
        heapq.heappush(edgelist,e)
    while len(edgelist):
        minedge = heapq.heappop(edgelist)
        #まだ使われてない頂点の中から最小の距離のものを探す
        if not used[minedge[1]]:
            continue
        v = minedge[1]
        d[v] = minedge[0]
        used[v] = False
        for e in edge[v]:
            if used[e[1]]:
                heapq.heappush(edgelist,[e[0]+d[v],e[1]])
    return d

n,w=map(int,input().split())#n:頂点数　w:辺の数

edge = [[] for i in range(n)] #edge[i] : iから出る道の[重み,行先]の配列
for i in range(w):
    x,y,z = map(int,input().split())
    x-=1
    y-=1
    for j in range(x+1,y+1):
        edge[x].append([z,j])
    for k in range(x,y):
        edge[y].append([z,k]) 
#print(edge)
print(dijkstra_heap(0)[-1])