import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.bigint, std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static File _f;
void file_io(string fn) { _f = File(fn, "r"); }
static string[] s_rd;
T _RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T _RD(T = long)(File f) { while(!s_rd.length) s_rd = f.readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
T[] _RDA(T = long)(T fix = 0) { auto r = readln.chomp.split.to!(T[]); r[] += fix; return r; }
T[] _RDA(T = long)(File f, T fix = 0) { auto r = f.readln.chomp.split.to!(T[]); r[] += fix; return r; }
T RD(T = long)() { if (_f.isOpen) return _RD!T(_f); else return _RD!T; }
T[] RDA(T = long)(T fix = 0) { if (_f.isOpen)  return _RDA!T(_f, fix); else return _RDA!T(fix); }

size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

void chmin(T)(ref T x, T y) { x = min(x, y); } void chmax(T)(ref T x, T y) { x = max(x, y); }
bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
T lcm(T)(T x, T y) { return x * (y / gcd(x, y)); }
double[] rotate(double[] vec, double rad) { return [cos(rad)*vec[0] - sin(rad)*vec[1], sin(rad)*vec[0] + cos(rad)*vec[1]]; }

//long mod = 10^^9 + 7;
long mod = 998_244_353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }
void modpow(ref long x, long y) { if (!y) { x = 1; return; } auto t = x; x.modpow(y>>1); x.modm(x); if (y&1) x.modm(t); }
void modd(ref long x, long y) { y.modpow(mod - 2); x.modm(y); }

struct SegTree(T)
{
	T delegate(const(T), const(T)) f;
	T[] data;
	T init;
    this(T[] _data, T delegate(const(T), const(T)) _f, T _init)
    {
		f = _f; init = _init;
		size_t n = 1; while (n < _data.length) n *= 2; data.length = n*2-1;
		foreach (i; 0.._data.length) data[i+n-1] = _data[i];
		foreach (i; _data.length..n) data[i+n-1] = _init;
		foreach_reverse (i; 0..n-1) data[i] = f(data[i*2+1], data[i*2+2]);
	}
    T query(size_t l, size_t r)
	{
        size_t n = (data.length+1) / 2; l += n-1; r += n-1; T res = init;
        while (l < r)
		{
            if ((l & 1) == 0) res = f(res, data[l]);
            if ((r & 1) == 0) res = f(res, data[r-1]);
            l = l/2; r = (r-1)/2;
        }
        return res;
    }
	void update(size_t i, T v)
	{
		i += (data.length+1) / 2 - 1; data[i] = v;
		while (i != 0) { i = (i-1)/2; data[i] = f(data[i*2+1], data[i*2+2]); }
    }
}

void main()
{
	auto N = RD;
	auto Q = RD;
	auto l = new long[](Q);
	auto r = new long[](Q);
	auto B = new long[](Q);
	foreach (i; 0..Q)
	{
		l[i] = RD-1;
		r[i] = RD;
		B[i] = RD;
	}

	auto index = l.MAKE_IDX;
	auto rbt = new RedBlackTree!(long[], "a[0] > b[0]", true);
	auto ans = new long[](N);
	ans[] = 1;
	foreach (i; 0..N)
	{
		while (!index.empty)
		{
			auto j = index.front;
			if (l[j] > i) break;
			rbt.insert([B[j], r[j]]);
			index.popFront;
		}
		
		while (!rbt.empty)
		{
			auto e = rbt.front;
			if (e[1] > i) break;
			rbt.removeFront;
		}
		if (rbt.empty) continue;
		auto e = rbt.front;
		ans[i] = e[0];
	}

	auto st = new SegTree!(long)(ans, (in long a, in long b)=>min(a, b), long.max);
	foreach (i; 0..Q)
	{
		auto e = st.query(l[i], r[i]);
		if (e != B[i])
		{
			ans.length = 0;
			break;
		}
	}

	if (ans.empty)
		writeln(-1);
	else
		ans.map!(to!string).join(" ").writeln;
	stdout.flush;
	debug readln;
}