const inf=99999;
 var e,c:array[1..1001] of longint;
     i,j,k,g,w:longint;
     mn:longint;
     a,b:array[1..5002] of longint;

begin
assign(input,'energii.in');
assign(output,'energii.out');
reset(input);
rewrite(output);

 readln(g);
 readln(w);
     mn:=inf;
  for i:=1 to g do
   begin
    read(e[i]); readln(c[i]);
   end;
   for i:=1 to 5001 do
    begin
     a[i]:=inf;
     b[i]:=inf;
    end;
     for i:=1 to g do
     if  a[e[i]]>c[i] then a[e[i]]:=c[i];


       for k:=1 to 5001 do
        b[k]:=a[k];

         for j:=1 to 5001 do
          begin
           for k:=1 to 5001 do
            b[k]:=a[k];
             for i:=1 to g do
              if j-e[i]>0 then
                           if a[j]>b[j-e[i]]+c[i] then a[j]:=b[j-e[i]]+c[i];
          end;

         for i:=w to 5001 do
          if mn>a[i] then mn:=a[i];
          write('-1');





close(input);
close(output);
end.