/* imports all std modules {{{*/
import
  std.algorithm,
  std.array,
  std.ascii,
  std.base64,
  std.bigint,
  std.bitmanip,
  std.compiler,
  std.complex,
  std.concurrency,
  std.container,
  std.conv,
  std.csv,
  std.datetime,
  std.demangle,
  std.encoding,
  std.exception,
  std.file,
  std.format,
  std.functional,
  std.getopt,
  std.json,
  std.math,
  std.mathspecial,
  std.meta,
  std.mmfile,
  std.net.curl,
  std.net.isemail,
  std.numeric,
  std.parallelism,
  std.path,
  std.process,
  std.random,
  std.range,
  std.regex,
  std.signals,
  std.socket,
  std.stdint,
  std.stdio,
  std.string,
  std.system,
  std.traits,
  std.typecons,
  std.uni,
  std.uri,
  std.utf,
  std.uuid,
  std.variant,
  std.zip,
  std.zlib;
/*}}}*/

/* libnum {{{*/
void amax(N, Args...)(ref N x, Args y) {
  x = x.max(y);
}
void amin(N, Args...)(ref N x, Args y) {
  x = x.min(y);
}
auto maxE(R)(R r) if (isInputRange!R) {
  ElementType!R x = r.front;
  r.popFront();
  foreach (y; r) x.amax(y);
  return x;
}
auto minE(R)(R r) if (isInputRange!R) {
  ElementType!R x = r.front;
  r.popFront();
  foreach (y; r) x.amin(y);
  return x;
}
/*}}}*/

/+---test
3 4
4 3
4 1
2 2
---+/
/+---test
5 3
1 2
1 3
1 4
2 1
2 3
---+/
/+---test
1 1
2 1
---+/

void main(string[] args) {
  long N, M;
  readf(" %d %d ", &N, &M);

  long[][] jobs;
  jobs.length = M;

  foreach (i; 0..N) {
    long day, reward;
    readf(" %d %d ", &day, &reward);
    if (M >= day) jobs[day-1] ~= reward;
  }

  auto queue = (new long[N]).heapify(0);

  long reward;
  foreach (job; jobs) {
    job.each!(x => queue.insert(x));
    if (queue.empty) continue;
    reward += queue.removeAny();
  }
  reward.writeln;
}
