DP

program classes;
var class:array [0..100] of longint;
    i,j,bh,judge:longint;
begin
  readln(m,n);
  fillchar(class,sizeof(class),0);
  for i:=1 to m do
  begin
    readln(bh,judge);
    class[i]:=class[bh]+judge;
  end;
  for i:=1 to m-1 do
    for j:=i+1 to m do
      if class[i]<class[j] then
      begin
        judge:=class[i];
        class[i]:=class[j];
        class[j]:=judge;
      end;
  judge:=0;
  for i:=1 to n do
    judge:=judge+class[i];
  writeln(judge);
end.

{需注意的是:
输入:第i行所用的"先修课程"只能在第1到i-1行中....}
{若想修改不足可先对输入数据按所用的"先修课程"从小到大排序.在做..}