#include <cstdio>
#include <algorithm>
using namespace std;
int d[5005],e[1005],c[1005];
int main()
{
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    int g,w,i,last=0,j;
    scanf("%d%d",&g,&w);
    for(i=1;i<=g;i++)
        scanf("%d%d",&e[i],&c[i]);
    for(i=1;i<=w;i++)
        d[i]=-1;
    for(i=1;i<=g;i++)
    {
        for(j=last;j>=0;j--)
        {
            if(d[j]!=-1)
            {
                if(j+e[i]<w)
                {
                    if(d[j+e[i]]!=-1)
                        d[j+e[i]]=min(d[j+e[i]],d[j]+c[i]);
                    else
                        d[j+e[i]]=d[j]+c[i];
                    if(j+e[i]>last)
                        last=j+e[i];
                }
                else
                {
                    if(d[w]!=-1)
                        d[w]=min(d[w],d[j]+c[i]);
                    else
                        d[w]=d[j]+c[i];
                    last=w;
                }
            }
        }
    }
    printf("%d",d[w]);
    return 0;
}