## https://yukicoder.me/problems/no/1675

MAX_INT = 10 ** 18

# ソースコードの出典URL: https://github.com/LyricalMaestro/at_coder_snippets/blob/af67863a2fe7f16cce8325bbc531f89968bfa525/src/segment_tree.py
class LazySegmentTree:
    """
    非再帰版遅延セグメント木。
    更新は「加法」、取得は「最大値」のもの限定。
    取得のところの都合で取得演算子は可換になっている必要がある。
    """

    def __init__(self, init_array):
        n = 1
        while n < len(init_array):
            n *= 2
        
        self.size = n
        self.array = [MAX_INT] * (2 * self.size)
        self.lazy_array = [0 for _ in range(2 * self.size)]
        for i, a in enumerate(init_array):
            self.array[self.size + i] = a
        
        end_index = self.size
        start_index = end_index // 2
        while start_index >= 1:
            for i in range(start_index, end_index):
                self.array[i] = min(self.array[2 * i], self.array[2 * i + 1])
            end_index = start_index
            start_index = end_index // 2
    
    def _propagates(self, *ids):
        for i in reversed(ids):
            self._propagate(i)

    def _propagate(self, i):
        v = self.lazy_array[i]
        if v == 0:
            return
        
        if i < self.size:
            self.lazy_array[2 * i] = v
            self.lazy_array[2 * i + 1] = v
            self.array[2 * i] = v
            self.array[2 * i + 1] = v
        self.lazy_array[i] = 0

    def _get_target_index(self, l, r):
        L = l + self.size; R = r + self.size
        lm = (L // (L & -L)) >> 1
        rm = (R // (R & -R)) >> 1
        while 0 < L and L < R:
            if R <= rm:
                yield R
            if L <= lm:
                yield L
            L >>= 1; R >>= 1
        while L > 0:
            yield L
            L >>= 1

    def set(self, l, r, x):
        # 2. 区間[l, r)のdata, lazyの値を更新
        L = self.size + l; R = self.size + r
        *ids, = self._get_target_index(l, r)
        self._propagates(*ids)
        while L < R:
            if R & 1:
                R -= 1
                self.lazy_array[R] = x
                self.array[R] = x
            if L & 1:
                self.lazy_array[L] = x
                self.array[L] = x
                L += 1
            L >>= 1; R >>= 1

        # 3. 伝搬させた区間について、ボトムアップにdataの値を伝搬する
        for i in ids:
            if i < self.size:
                self.array[i] = min(self.array[2 * i], self.array[2 * i +  1])

    def get_min(self, l, r):
        # 1. トップダウンにlazyの値を伝搬
        self._propagates(*self._get_target_index(l, r))
        L = self.size + l; R = self.size + r

        # 2. 区間[l, r)の最大値を求める
        s = MAX_INT
        while L < R:
            if R & 1:
                R -= 1
                s = min(s, self.array[R])
            if L & 1:
                s = min(s, self.array[L])
                L += 1
            L >>= 1; R >>= 1
        return s


def main():
    N, Q = map(int, input().split())
    lrb = []
    for _ in range(Q):
        l, r, b = map(int, input().split())
        lrb.append((l - 1, r -1 , b))

    lrb.sort(key=lambda x: x[2])

    lazy_seg_tree = LazySegmentTree([1] * N)
    for l, r, b in lrb:
        lazy_seg_tree.set(l, r + 1, b)

    for l, r, b in lrb:
        b0 = lazy_seg_tree.get_min(l, r + 1)
        if b0 != b:
            print(-1)
            return

    answer = []
    for i in range(N):
        answer.append(lazy_seg_tree.get_min(i, i +1))
    print(" ".join(map(str, answer)))









if __name__ == "__main__":
    main()