#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9;

int ans[5005];

int main(void){
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    for(int i=1; i<5005; ++i) ans[i]=INF;

    int g,n,e,c,l=0,r=INF;
    scanf("%d%d",&g,&n);
    for(int i=0; i<g; ++i){
        scanf("%d%d",&e,&c);
        for(int j=l; j>=0; --j){
            if(ans[j]==-1)
                continue;
            if(j+e>=n){
                l=n;
                r=min(r, ans[j]+c);
            }
            else {
                l=max(l,j+e);
                ans[j+e]=min(ans[j+e], ans[j]+c);
            }
        }
    }
    if(r==INF)
        printf("-1");
    else
        printf("%d",r);
    return 0;
}