#include<fstream>
using namespace std;
ifstream cin("energii.in");
ofstream cout("energii.out");
int G, W, a[10010],x,y;
int main(){
	cin >> G >> W;
	for(int i = 0; i<=W;i++)
		a[i] = 10000000;
	for (int i = 0 ; i < G; i++){
		cin >> x >>y;
		if (x >= W){
			if (a[W]>y){
				a[W] = y;
			}
		}
		for(int j = W; j>0;j--){
			if (j<x){
				a[j]=min(a[j],y);
			}else {
				a[j]=min(a[j-x]+y,a[j]);
			}
		}
	}
	if (a[W]==10000000){cout<<"-1";return (0);}
	cout <<a[W];
}