#include<stdio.h>
#include<stdlib.h>
int g,w,e[10001],c[10001];
int main(){
	int i;
	FILE *fin=fopen("energii.in","r");
	fscanf(fin,"%d",&g);
	fscanf(fin,"%d",&w);
	for(i=1;i<g;i++)
		fscanf(fin,"%d %d",&e[i],&c[i]);
	int sum=0;
	for(i=1;i<g;i++)
		sum+=e[i];
	FILE *fout=fopen("energii.out","w");
	if(sum<w)
		fprintf(fout,"-1\n");
	return 0;
}