#include <bits/stdc++.h>
#define DM 10005
#define pii pair<int,int>
#define x first
#define y second
#define INF 0x3f3f3f3f
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int n,w,dp[DM],en,pr;

int main()
{
    fin>>n>>w;
    for(int i=1;i<DM;++i)
        dp[i]=INF;
    for(int i=1;i<=n;++i){
        fin>>en>>pr;
        for(int j=w;j>=1;--j){
            if(j<en)
                dp[j]=min(dp[j],pr);
            else if(dp[j-en]!=INF){
                int mn1 = min(dp[j],dp[j-en]+pr);
                dp[j]=min(dp[j+1],mn1);
            }
        }
    }
    if(dp[w]!=INF) fout<<dp[w];
    else fout<<"-1";
    return 0;
}