#include<bits/stdc++.h>

using namespace std;

int g,w,ss;
int e[1100],c[1100],d[1100][5100];


int main(){
	ifstream cin("energii.in");
	//ofstream cout("energii.out");
	cin>>g>>w;
	for(int i=1;i<=g;i++){
		cin>>e[i]>>c[i];
	}
	for(int j=0;j<=w;j++)
		d[0][j]=20000;
	for(int i=1;i<=g;i++){
		for(int j=1;j<=w;j++){
			if(e[i]<=j) d[i][j]=min(d[i-1][j],d[i-1][j-e[i]]+c[i]);
			else d[i][j]=min(d[i-1][j],c[i]);	
		}
	}
	if(d[g][w]!=20000) cout<<d[g][w]; else cout<<-1;
	return 0;
}