#include<bits/stdc++.h>
using namespace std;
long long n,E,e,c,dp[3][5010];
int main(){
    ifstream cin("energii.in");
    ofstream cout("energii.out");
    cin>>n>>E;
    for(int i = 1;i<=E;i++)
        dp[0][i] = 2e9;
    for(int i = 1;i<=n;i++){
        cin>>e>>c;
        for(int j = 1;j<=E;j++){
            if(j - e <0){
                dp[1][j] = min(dp[0][j], c);
            }
            else{
                dp[1][j] = min(dp[0][j], dp[0][j - e] + c);
            }
        }
        for(int j = 1;j<=E;j++)
            dp[0][j] = dp[1][j];
    }

    if(dp[1][E] == 2e9) cout<<-1;
    else cout<<dp[1][E];
    return 0;
}