const lmax=12000;
var a,b:array[1..lmax]of longint;
    min,g,w,e,c,i,j:longint;

begin
assign(input,'energii.in');
reset(input);
fillchar(a,sizeof(a),0);
readln(g,w);
readln(e,c);
a[e]:=c;
for i:=2 to g do begin
    fillchar(b,sizeof(b),0);
    readln(e,c);
    for j:=1 to lmax-e do
       if(a[j]<>0)then
                    b[j+e]:=a[j]+c;
    for j:=1 to lmax do
       if(a[j]<>0)and(a[j]<b[j])or(b[j]=0) then b[j]:=a[j];
    if(c<b[e])or(b[e]=0) then b[e]:=c;
    a:=b;
    end;
min:=maxlongint;
for i:=w to lmax do
  if (a[i]<>0)and(a[i]<min) then min:=a[i];
close(input);
assign(output,'energii.out');
rewrite(output);
if min<>maxlongint then
       writeln(min)
else
 writeln(-1);
close(output);
end.