Program p1;
const limit=100000000;
var fi,fo :text;
    i,g,j,w : longint;
    c: array[-2..1009,-2..5009] of longint;
    eg,cost : array[-2..1009] of integer;

Function min(a,b : longint):longint;
begin
    if a<b then min:=a
           else min:=b;
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 c[i,j]:=limit;

    for i:=1 to g do
          for j:=1 to w do if eg[i]<j then c[i,j]:=min(c[i-1,j],c[i-1,j-eg[i]]+cost[i])
                                     else c[i,j]:=min(c[i-1,j],cost[i]);


    if c[g,w]=limit then write(fo,'-1')
                    else write(fo,c[g,w]);

    close(fi); close(fo);
end.