type sir= array [1..1001] of integer;
var put,cost: sir;
    n,p,cost1,cost2,put1,put2: integer;
    i,j: integer;
    ok: boolean;


procedure citire(var put,cost: sir; var n,p: integer);
var f: text;
    i: integer;
begin
    assign(f,'energii.in'); reset(f);
    readln(f,n);
    readln(f,p);
    for i:= 1 to n do readln(f,put[i],cost[i]);
    close(f);
end;

function verif: boolean;
var i: integer;
    s: qword;
begin
    verif:=false;
    for i:= 1 to n do
        s:= s+put[i];
    if s>p then verif:=true;
end;


procedure tip(cost1: integer);
var f: text;
begin
    assign(f,'energii.out'); rewrite(f);
    writeln(f,cost1);
    close(f);
end;




begin{pp}
citire(put,cost,n,p);
cost2:=0;
put2:=0;
ok:=verif;
if not ok then tip(-1) else tip(0);
end.