#include <fstream>
#include <iostream>
#include <algorithm>

std::ifstream f("energii.in");
std::ofstream g("energii.out");

/*int * a = new int[10001];
int * b = new int[10001];*/

int matrix[1003][5003];

int cost[5003];
int energ[5003];
int G,W;

long testSum;

void read(){
	f >> G;
	f >> W;
	for(int i = 1 ; i <= G ; ++i){
		f >> energ[i] >> cost[i];
		testSum += energ[i];
	}
}

int main(){
	read();

	
	if(testSum < W){
		g <<"-1";
	}else{

	}

	f.close();
	g.close();
	return 0;
	
}