program energii_2;
const inf = 100000000;
 var a: array [0..1005,0..5005] of longint;
    eg,cost: array [1..1005] of integer;
    i,j,n,m,g,w:integer;
    fi,fo:text;
 function min(a,b:longint):longint;
 begin
  if a>b then min:=b
           else min:=a;
 end;
begin
assign(fi,'energii.in');
 reset(fi);
assign(fo,'energii.out');
 rewrite(fo);
 readln(fi,g);
  readln(fi,w);
 for i:=1 to g do
   readln(fi,eg[i],cost[i]);
 for i:=0 to g do
  for j:=0 to w do
          a[i,j]:=inf;
 for i:=1 to g do
  for j:=1 to w do
   if eg[i]<=j then
      a[i,j]:=min(a[i-1,j],a[i-1,j-eg[i]]+cost[i])
       else a[i,j]:=min(a[i-1,j],cost[i]);
 if a[g,w]=inf then write(fo,'-1')
  else write(fo,a[g,w]);
close(fo);
end.