// URL: https://yukicoder.me/problems/no/655

import std.algorithm, std.array, std.container, std.math, std.range, std.typecons, std.string;

version(unittest) {} else
void main()
{
  int N, K; long P; io.getV(N, K, P);
  Point[] b; io.getS!("x", "y")(K, b);
  foreach (ref bi; b) { --bi.x; --bi.y; }

  if (N == 1) { io.put(0); return; }

  auto a = kaidan!long(N);
  foreach (ref ai; a) ai[] = -1;

  auto q = DList!Point(b);
  auto dp = [Point(-1, -1), Point(-1, 0), Point(0, -1), Point(0, 1), Point(1, 0), Point(1, 1)];
  foreach (ref bi; b) a[bi.x][bi.y] = 0;
  while (!q.empty) {
    auto pp = q.front; q.removeFront;
    foreach (dpi; dp) {
      auto np = pp + dpi;
      if (np.x < 0 || np.x >= N || np.y < 0 || np.y > np.x || a[np.x][np.y] >= 0) continue;
      a[np.x][np.y] = a[pp.x][pp.y] + 1;
      q.insertBack(np);
    }
  }

  auto as = kaidan!long(N+1);
  foreach_reverse (i; 0..N)
    foreach (j; 0..i+1) {
      as[i][j] = as[i+1][j] + as[i+1][j+1] + a[i][j];
      if (i < N-1) as[i][j] -= as[i+2][j+1];
    }

  auto bs = kaidan2!long(N+1);
  foreach_reverse (i; 0..N)
    foreach (j; 0..i+1)
      bs[i][j+1] = bs[i][j]+bs[i+1][j+1]-bs[i+1][j]+a[i][j];

  auto calc(int i, int j, int e)
  {
    if (e == 0) return a[i][j];
    else return as[i][j]-as[i+e+1][j+e+1]-bs[i+e+1][j+e+1]+bs[i+e+1][j];
  }

  auto e = kaidan!int(N);
  foreach (j; 0..N) e[N-1][j] = as[N-1][j] >= P ? 0 : 1;

  foreach_reverse (i; 0..N-1)
    foreach (j; 0..i+1) {
      auto r = min(e[i+1][j], e[i+1][j+1]);
      while (r >= 0 && calc(i, j, r) >= P) --r;
      e[i][j] = r+1;
    }

  auto ans = 0L;
  foreach (i; 0..N)
    foreach (j; 0..i+1)
      ans += N-(e[i][j]+i);

  io.put(ans);
}

auto kaidan(T)(int n)
{
  auto a = new T[][](n);
  foreach (i; 0..n) a[i] = new T[](i+1);
  return a;
}

auto kaidan2(T)(int n)
{
  auto a = new T[][](n);
  foreach (i; 0..n) a[i] = new T[](i+2);
  return a;
}

alias Point = Point2!int;
struct Point2(T)
{
  alias P = Point2!T, Op = string;
  T x, y;
  pure P opBinary(Op o)(P r) if (o=="+"||o=="-")
  { return mixin("P(x"~o~"r.x, y"~o~"r.y)"); }
  P opOpAssign(Op o)(P r) if (o=="+"||o=="-")
  { mixin("x"~o~"=r.x; y"~o~"=r.y;"); return this; }
  pure P opBinary(Op o)(T a) if (o=="*"||o=="/")
  { return mixin("P(x"~o~"a, y"~o~"a)"); }
  P opOpAssign(Op o)(T a) if (o=="*"||o=="/")
  { mixin("x"~o~"=a; y"~o~"=a;"); return this; }
  pure T opBinary(Op o: "*")(P r) { return x*r.x+y*r.y; }
  pure T hypot2() { return x^^2+y^^2; }
}

pure T distManhattan(T)(Point2!T p1, Point2!T p2)
{ return (p1.x-p2.x).abs + (p1.y-p2.y).abs; }

pure T cross(T)(Point2!T p1, Point2!T p2)
{ return p1.x*p2.y - p1.y*p2.x; }

struct Point3(T)
{
  alias P = Point3!T, Op = string;
  T x, y, z;
  pure P opBinary(Op o)(P r) if (o=="+"||o=="-")
  { return mixin("P(x"~o~"r.x, y"~o~"r.y, z"~o~"r.z)"); }
  P opOpAssign(Op o)(P r) if (o=="+"||o=="-")
  { mixin("x"~o~"=r.x; y"~o~"=r.y; z"~o~"=r.z;"); return this; }
  pure P opBinary(Op o)(T a) if (o=="*"||o=="/")
  { return mixin("P(x"~o~"a, y"~o~"a, z"~o~"a)"); }
  P opOpAssign(Op o)(T a) if (o=="*"||o=="/")
  { mixin("x"~o~"=a; y"~o~"=a; z"~o~"=a;"); return this; }
  pure T opBinary(Op o: "*")(P r) { return x*r.x+y*r.y+z*r.z; }
  pure T hypot2() { return x^^2+y^^2+z^^2; }
}

pure Point3!T cross(T)(Point3!T p1, Point3!T p2)
{ return Point3!T(p1.y*p2.z - p1.z*p2.y, p1.z*p2.x - p1.x*p2.z, p1.x*p2.y - p1.y*p2.x); }

auto io = IO!()();
import std.stdio;
struct IO(string floatFormat = "%.10f", string delimiter = " ", alias IN = stdin, alias OUT = stdout)
{
  import std.conv, std.format, std.meta, std.traits;
  alias assignable = hasAssignableElements;

  auto getV(T...)(ref T v) { foreach (ref w; v) get(w); }
  auto getA(T)(size_t n, ref T v) if (assignable!T) { v = new T(n); foreach (ref w; v) get(w); }
  auto getC(T...)(size_t n, ref T v) if (allSatisfy!(assignable, T))
  {
    foreach (ref w; v) w = new typeof(w)(n);
    foreach (i; 0..n) foreach (ref w; v) get(w[i]);
  }
  auto getM(T)(size_t r, size_t c, ref T v) if (assignable!T && assignable!(ElementType!T))
  {
    v = new T(r); foreach (ref w; v) getA(c, w);
  }
  template getS(E...)
  {
    auto getS(T)(size_t n, ref T v)
    {
      v = new T(n); foreach (ref w; v) foreach (e; E) mixin("get(w."~e~");");
    }
  }

  auto put(bool flush = false, T...)(T v)
  {
    foreach (i, w; v) { putA(w); if (i < v.length-1) OUT.write(delimiter); }
    OUT.writeln;
    static if (flush) OUT.flush();
  }
  auto putB(S, T)(bool c, S t, T f) { if (c) put(t); else put(f); }
  auto putRaw(T...)(T v) { OUT.write(v); OUT.writeln; }

  private
  {
    dchar[] buf;
    auto sp = (new dchar[](0)).splitter;
    void nextLine() { IN.readln(buf); sp = buf.splitter; }
    auto get(T)(ref T v) { if (sp.empty) nextLine(); v = sp.front.to!T; sp.popFront(); }

    auto putR(T)(T v)
    {
      auto w = v;
      while (!w.empty) { putA(w.front); w.popFront(); if (!w.empty) OUT.write(delimiter); }
    }
    auto putA(T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putR(v);
      else if (isFloatingPoint!T) OUT.write(format(floatFormat, v));
      else OUT.write(v);
    }
  }
}