#include <fstream>

using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int c[1001][5001];
int main()
{int i,j,G,w,e[1001],c1[1001],s1=0;
 fin>>G>>w;
 for(i=1;i<=G;i++)
 {fin>>e[i]>>c1[i];
 s1=s1+e[i];}
 if (s1<w) fout<<-1;
 else
 {for(i=0;i<=w;i++)
    c[0][i]=20000000;

  for(i=0;i<=G;i++)
  c[i][0]=20000000;

for(i=1;i<=G;i++)
 for(j=1;j<=w;j++)
  if (e[i]>=j) c[i][j]=min(c1[i],c[i-1][j]);
    else c[i][j]=min(c1[i]+c[i-1][j-e[i]],c[i-1][j]);

 fout<<c[G][w];
 }








fin.close();
fout.close();
  return 0;
}