var cstt,aux,j,i,g,w:integer;
a,b:array[1..1002] of integer;
f,h:text;
s:longint;
begin
assign(f,'energii.in');reset(f);
assign(output,'energii.out');rewrite(output);
readln(f,g);
readln(f,w);
for i:=1 to g do
readln(f,a[i],b[i]);
for i:=1 to g-1 do
for j:=i+1 to g do
if a[i]<a[j] then
begin
aux:=b[i];
b[i]:=b[j];
b[j]:=aux;
aux:=a[i];
a[i]:=a[j];
a[j]:=aux;
end;
i:=1;
cstt:=0;
for i:=1 to g do
s:=s+b[i];
if s<w then write(g,'-1')
else
begin
while w>0 do
begin
w:=w-a[i];
cstt:=cstt+b[i];
end;
write(output,cstt);
end;
close(f);
close(output);
end.