n,q = map(int,input().split())
lr = [[int(i)-1 for i in input().split()] for j in range(q)]

lr.sort(key=lambda x:x[2], reverse=True)

li = [10**9]*n
s = set(i for i in range(n))
sm = set()

for i in range(q):
    l,r,b = lr[i]
    if i > 0 and lr[i-1][2] != b:
        sm = set()
    a = set(l+i for i in range(r-l+1))
    f = False
    for i in a&s:
        f = True
        li[i] = b+1
        s.remove(i)
        sm.add(i)
    if f == False:
        if not sm&a:
            print(-1)
            exit()
    
print(*li)