#include<bits/stdc++.h>
#include<atcoder/all>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;

int main(){
	int N;
	long long M;
	cin >> N >> M;
	vector<pair<long long, long long>> target;
	assert(N >= 1 && N <= 100000);
	assert(M >= 2 && M <= 1000000000000000000);
	rep(i, N){
		long long l, r;
		cin >> l >> r;
		if(cin.fail()) assert(false);
		target.emplace_back(l, r);
		assert(1 <= l && l < r && r <= M);
	}
	cout << "-1\n";
	return 0;
}