from atcoder.segtree import SegTree

N,Q = map(int,input().split())
INF = 10 ** 9

LRB = [list(map(int,input().split())) for _ in range(Q)]
LRB.sort(key = lambda x:(x[1],x[0]))
INF = 10 ** 9
prer = -1
prev = INF
A = [INF] * (N + 1)
ST = SegTree(min, INF, A)

for l,r,b in LRB:
    x = ST.prod(l-1,r)
    if x < b:
        print(-1)
        exit()
    elif x > b:
        if prer < l - 1:
            A[l - 1] = b
            ST.set(l - 1, b)
            prer = r - 1
        else:
            if prev > b:
                if prer + 1 < N:
                    A[prer + 1] = b
                    ST.set(prer + 1, b)
                else:
                    print(-1)
                    exit()
            else:
                A[l - 1] = b
                ST.set(l-1,b)
    prev = b
    prer = r - 1

print(*A[:N])