var n,i,j,w,x,y,p,x1,aux:integer;
    f,g:text;
    s:array[0..1001,0..5001]of longint;
function min(a,b:longint):longint;
begin
if a<b then min:=a
       else min:=b;
end;
function maxi(a,b:longint):longint;
begin
if a>b then maxi:=a
       else maxi:=b;
end;
begin
assign(f,'energii.in');reset(f);assign(g,'energii.out');rewrite(g);
read(f,n,w);  p:=0;
for i:=1 to w do  begin s[0,i]:=1500000;  s[1,i]:=1500000; end;
for i:=1 to n do
  begin
    read(f,x,y);
    for j:=1 to w do
       s[i,j]:=min(s[i-1,j],s[i-1,maxi(j-x,0)]+y);
  end;
if s[n,w]<1500000 then write(g,s[n,w]) else write(g,-1);
close(f);close(g);
end.