def main():
    from sys import stdin
    input = stdin.readline

    import numpy as np
    n, m = map(int, input().split())
    abc = [list(map(int, input().split())) for _ in [0]*m]
    g = [[] for _ in [0]*n]
    [g[u-1].append([v-1, c]) for u, v, c in abc]
    [g[i+1].append([i, 0]) for i in range(n-1)]

    import heapq

    yen = np.full(n, np.inf)
    h = [(0, 0)]
    heapq.heapify(h)
    while h:
        d, i = heapq.heappop(h)
        if yen[i] == np.inf:
            yen[i] = d
            for x, y in g[i]:
                heapq.heappush(h, (d+y, x))
    print(int(yen[n-1]))


main()
