Problem:
Score : 700 points

Problem Statement

Given are positive integers N and K.

Determine if the 3N integers K, K+1, ..., K+3N-1 can be partitioned into N triples (a_1,b_1,c_1), ..., (a_N,b_N,c_N) so that the condition below is satisfied. Any of the integers K, K+1, ..., K+3N-1 must appear in exactly one of those triples.

For every integer i from 1 to N, a_i + b_i \leq c_i holds.

If the answer is yes, construct one such partition.

Constraints

1 \leq N \leq 10^5

1 \leq K \leq 10^9

Input

Input is given from Standard Input in the following format:

N K

Output

If it is impossible to partition the integers satisfying the condition, print -1. If it is possible, print N triples in the following format:

a_1 b_1 c_1
:
a_N b_N c_N

Sample Input 1

1 1

Sample Output 1

1 2 3

Sample Input 2

3 3

Sample Output 2

-1

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;

long long N, K;
vector<long long> a;
vector<long long> b;
vector<long long> c;

int main(){
	cin >> N >> K;

	for(long long i = 0; i < N; i++){
		a.push_back(K + 2 * i);
		b.push_back(K + 2 * i + 1);
	}

	for(long long i = K + 2 * N; i < K + 3*N; i++){
		c.push_back(i);
	}

	for(long long i = 0; i < N; i++){
		if(a[i] + b[i] > c[i]){
			cout << "-1" << endl;
			return 0;
		}
	}

	for(long long i = 0; i < N; i++){
		cout << a[i] << " " << b[i] << " " << c[i] << endl;
	}
}