#include <fstream>
#define inf 10002
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int n,P,v[1001],c[1001],s[10001];

int main()
{
    int i,j;
    fin>>n>>P;
    for (i=1;i<=n;i++) fin>>v[i]>>c[i];
    for (i=1;i<=P;i++) s[i]=inf;
    for (i=1;i<=n;i++)
    {
    for (j=P;j-v[i]>=0;j--)  if (s[j-v[i]]+c[i]<s[j]) s[j]=s[j-v[i]]+c[i];
    for (j=1;j<v[i];j++) if (c[i]<s[j]) s[j]=c[i];
    }
    if (s[P]==inf) fout<<-1;
    else fout<<s[P];
}