program rival(input,output);
var
 i,j,k,head:longint;
 t1,t2:longint;
 n,m,x,y,ans:longint;
 w,t:array[1..50]of longint;
 w1,p1:array[1..1000]of longint;
 tt:array[1..50]of boolean;
 f:array[0..101,0..101]of longint;

function max(a,b:longint):longint;
begin
 if a>b then max:=a else max:=b;
end;

begin
 assign(input,'rival.in');
 reset(input);
 readln(t1,t2);
 readln(n,m);
 for i:=1 to n do
 begin
  readln(w[i],t[i]);
  ans:=ans+w[i];
  if (t[i]>t1)and(t[i]*2>t2) then
   tt[i]:=true;
 end;
 close(input);

 for i:=1 to n do
  if tt[i]=false then
  begin
   inc(head);
   w1[head]:=w[i];
   p1[head]:=t[i];
  end;

 for i:=1 to head do
  for j:=t1 downto 0 do
   for k:=t2 downto 0 do
   begin
    if j-p1[i]>=0 then
    f[j,k]:=max(f[j,k],f[j-p1[i],k]+w1[i]);
    if k-2*p1[i]>=0 then
    f[j,k]:=max(f[j,k],f[j,k-2*p1[i]]+w1[i]);
   end;

 assign(output,'rival.out');
 rewrite(output);
 writeln(ans-f[t1,t2]);
 close(output);
end.