#include<bits/stdc++.h>
using namespace std;
#define INF 99999999

ifstream in("energii.in");
ofstream out("energii.out");
int elemente,profit[1001],cost[1001];
int capacitate;

void read()
{
    in>>elemente>>capacitate;
    for(int i=0; i<elemente; i++)
    {
        in>>profit[i]>>cost[i];
    }
}

int dp[1002][5002];


int knapsack(int index,int cap)
{

    if(index==-1 && cap>0)
    {
        return 99999999;
    }
    if(cap<=0)
    {
        return 0;
    }
    else
    {
        int a=knapsack(index-1,cap);
        int b=cost[index]+knapsack(index-1,cap-profit[index]);
        return min(a,b);
    }


}


int dpp()
{
    for(int i=0; i<elemente; i++)
    {
        for(int k=0; k<=capacitate; k++)
        {
            if(i==0)
            {
                if(profit[i]<k)
                {
                    dp[i][k]=INF;
                }
                else
                    dp[i][k]=cost[0];
            }
            else
            {
                int rest=k-profit[i];
                int a=0;
                if(rest>0)
                    a=dp[i-1][rest];
                dp[i][k]=min(cost[i]+a, dp[i-1][k]);
            }
        }
    }

    int result=dp[elemente-1][capacitate];
    if(result==INF)
        out<<-1;
    else
        out<<result;


}


int main()
{
    read();
    dpp();


}