mod = 1000000007
eps = 10**-9


def main():
    import sys
    from heapq import heappush, heappop
    input = sys.stdin.buffer.readline

    # min
    def STfunc(a, b):
        if a < b:
            return a
        else:
            return b

    # クエリは0-indexedで[l, r)
    class SparseTable():
        def __init__(self, A):
            # A: 処理したい数列
            self.N = len(A)
            self.K = self.N.bit_length() - 1
            self.table = [0] * (self.N * (self.K + 1))
            for i, a in enumerate(A):
                self.table[i] = a
            for k in range(1, self.K + 1):
                for i in range(self.N):
                    j = i + (1 << (k - 1))
                    if j <= self.N - 1:
                        self.table[i + k * self.N] = STfunc(self.table[i + (k - 1) * self.N],
                                                            self.table[j + (k - 1) * self.N])

        def query(self, l, r):
            # [l, r)の最小値を求める
            k = (r - l).bit_length() - 1
            return STfunc(self.table[l + k * self.N], self.table[r - (1 << k) + k * self.N])

    N, Q = map(int, input().split())
    pq = []
    imos = [[] for _ in range(N+1)]
    query = []
    for _ in range(Q):
        l, r, b = map(int, input().split())
        query.append((l, r, b))
        imos[l-1].append(b)
        imos[r].append(-b)
    ans = [10 ** 9] * N
    cnt = {}
    for i in range(N):
        for b in imos[i]:
            if b > 0:
                heappush(pq, -b)
                if b not in cnt:
                    cnt[b] = 0
                cnt[b] += 1
            else:
                cnt[-b] -= 1
        a = -1
        while pq:
            aa = -pq[0]
            if cnt[aa] == 0:
                heappop(pq)
            else:
                a = aa
                break
        if a != -1:
            ans[i] = a

    ok = 1
    ST = SparseTable(ans)
    for l, r, b in query:
        if ST.query(l-1, r) != b:
            ok = 0
            break
    if ok:
        print(*ans)
    else:
        print(-1)


if __name__ == '__main__':
    main()