#include <cstdio>
#include<cstring>
using namespace std;
int d1[5005],d2[5005];
int min(int a,int b)
{
    if(a>b)
        return b;
    return a;
}
int main()
{
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);

    int g,E,i,j,e,c;
    scanf("%d%d",&g,&E);

    scanf("%d%d",&e,&c);
        for(j=1;j<=E;j++)
            if(e>=j)
                d1[j]=c;
            else
                d1[j]=-1;
    memcpy(d2,d1,sizeof(d1));

    for(i=2;i<=g;i++)
    {
        scanf("%d%d",&e,&c);
        for(j=1;j<=E;j++)
            if(e>=j)
                if(d2[j]==-1)
                    d1[j]=c;
                else
                    d1[j]=min(c,d2[j]);
            else
                if(d2[j-e]!=-1)
                    d1[j]=min(c+d2[j-e],d2[j]);
                else
                    d1[j]=-1;

        memcpy(d2,d1,sizeof(d1));
    }
    printf("%d",d2[E]);
    return 0;
}