class LazySegTree_RUQ:
    def __init__(self,init_val,segfunc,ide_ele):
        n = len(init_val)
        self.segfunc = segfunc
        self.ide_ele = ide_ele
        self.num = 1<<(n-1).bit_length()
        self.tree = [ide_ele]*2*self.num
        self.lazy = [None]*2*self.num
        for i in range(n):
            self.tree[self.num+i] = init_val[i]
        for i in range(self.num-1,0,-1):
            self.tree[i] = self.segfunc(self.tree[2*i],self.tree[2*i+1])
    def gindex(self,l,r):
        l += self.num
        r += self.num
        lm = l>>(l&-l).bit_length()
        rm = r>>(r&-r).bit_length()
        while r>l:
            if l<=lm:
                yield l
            if r<=rm:
                yield r
            r >>= 1
            l >>= 1
        while l:
            yield l
            l >>= 1
    def propagates(self,*ids):
        for i in reversed(ids):
            v = self.lazy[i]
            if v is None:
                continue
            self.lazy[i] = None
            self.lazy[2*i] = v
            self.lazy[2*i+1] = v
            self.tree[2*i] = v
            self.tree[2*i+1] = v
    def update(self,l,r,x):
        ids = self.gindex(l,r)
        self.propagates(*self.gindex(l,r))
        l += self.num
        r += self.num
        while l<r:
            if l&1:
                self.lazy[l] = x
                self.tree[l] = x
                l += 1
            if r&1:
                self.lazy[r-1] = x
                self.tree[r-1] = x
            r >>= 1
            l >>= 1
        for i in ids:
            self.tree[i] = self.segfunc(self.tree[2*i], self.tree[2*i+1])
    def query(self,l,r):
        ids = self.gindex(l,r)
        self.propagates(*self.gindex(l,r))
        res = self.ide_ele
        l += self.num
        r += self.num
        while l<r:
            if l&1:
                res = self.segfunc(res,self.tree[l])
                l += 1
            if r&1:
                res = self.segfunc(res,self.tree[r-1])
            l >>= 1
            r >>= 1
        return res
    
def main():
    #####segfunc#####
    def segfunc(x, y):
        return min(x, y)
    #################

    #####ide_ele#####
    ide_ele = 10**9
    #################
    
    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])
    
    a = [10**9]*n

    seg = LazySegTree_RUQ(a, segfunc=segfunc, ide_ele=ide_ele)

    for i in range(q):
        #lo = seg.query(lr[i][0],lr[i][1]+1)
        seg.update(lr[i][0],lr[i][1]+1,lr[i][2]+1)
    
    for i in range(q):
        b = seg.query(lr[i][0],lr[i][1]+1)
        if b != lr[i][2]+1:
            print(-1)
            exit()
    exit()
    
    b = [10**9]*n
    for i in range(n):
        b[i] = seg.query(i,i+1)
    
    print(*b)

if __name__ == '__main__':
    main()