/*****************

    ~LeTeutz~

*****************/

#include <bits/stdc++.h>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");

const int INF=20001;
int N,E;
int e[1001],c[1001];
int dp[2][5001];

int main()
{
    f>>N>>E;
    for(int i=1; i<=N; i++)
        f>>e[i]>>c[i];

    for(int i=1; i<=E; i++)
        dp[0][i] = INF;

    bool ok = 0;
    for(int i=1; i<=N; i++){
        for(int j=1; j<=E; j++){
            if( j-e[i] < 1)
                dp[1-ok][j] = min( dp[ok][j] , c[i]);
            else{
                dp[1-ok][j] = min( dp[ok][j] , dp[ok][j-e[i]] + c[i]);
            }
        }
        ok=!ok;
    }

    if( dp[ok][E] != INF)
        g<<dp[ok][E]<<"\n";
    else
        g<<-1<<"\n";
    return 0;
}