const inf=99999;
 var g,w:integer;
     e,c:array[1..1001] of integer;
     i,j,k:integer;
     a,b:array[1..5001] of longint;

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

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


       for k:=1 to w do
        b[k]:=a[k];
         for j:=1 to w do
          begin
           for k:=1 to w 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;


           if a[w]=inf then write('-1') else write(a[w]);




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