#include<cstdio>
unsigned G,w,i,min,ex,EG[10001],CG[10001];
int main(){
    FILE*f=fopen("energii.in","r");
    FILE*h=fopen("energii.out","w");
    fscanf(f,"%u",&G);
	fscanf(f,"%u",&w);
	for(i=0;i<G;i++){
		fscanf(f,"%u %u",&EG[i],&CG[i]);
		if(EG[i]>=w) min=CG[i];
	}
	if(min<w&&w!=0){
		while(ex<w){
			min+=CG[i];
			ex+=EG[i];
			i++;
		}
	}
	if(min<w&&w!=0) fprintf(h,"-1");
	else fprintf(h,"%u",min);
   
    fclose(f);fclose(h);
    return 0;
}