// URL: https://yukicoder.me/problems/no/199

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

version(unittest) {} else
void main()
{
  Point[] p; io.getS!("x", "y")(5, p);
  io.putB(p.convexHull.length == 5, "YES", "NO");
}

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); }

pure Point2!T[] convexHull(T)(Point2!T[] p)
{
  p.multiSort!("a.x < b.x", "a.y < b.y");

  Point2!T[] lower;
  foreach (pi; p) {
    while (lower.length >= 2 && cross(lower[$-2]-pi, lower[$-1]-pi) <= 0)
      lower.length -= 1;
    lower ~= pi;
  }

  Point2!T[] upper;
  foreach_reverse (pi; p) {
    while (upper.length >= 2 && cross(upper[$-2]-pi, upper[$-1]-pi) <= 0)
      upper.length -= 1;
    upper ~= pi;
  }

  return (lower.dropBackOne ~ upper.dropBackOne).array;
}

pure T convexHullDiameter2(T)(Point2!T[] p)
{
  auto n = p.length;
  size_t ps, pt;
  foreach (i; 1..n) {
    if (p[i].y > p[ps].y) ps = i;
    if (p[i].y < p[pt].y) pt = i;
  }

  auto maxD = (p[ps]-p[pt]).hypot2;
  auto i = ps, j = pt;
  do {
    auto ni = (i+1) % n, nj = (j+1) % n;
    if (cross(p[ni]-p[i], p[nj]-p[j]) < 0)
      i = ni;
    else
      j = nj;
    maxD = max(maxD, (p[i]-p[j]).hypot2);
  } while (i != ps || j != pt);

  return maxD;
}

auto io = IO!()();
import std.stdio;
struct IO(alias IN = stdin, alias OUT = stdout)
{
  import std.conv, std.format, std.meta, std.traits, core.stdc.stdlib;

  auto getV(T...)(ref T v) { foreach (ref w; v) get(w); }
  auto getA(T)(size_t n, ref T v) if (hasAssignableElements!T)
  { v = new T(n); foreach (ref w; v) get(w); }
  auto getC(T...)(size_t n, ref T v)
  if (allSatisfy!(hasAssignableElements, 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 (hasAssignableElements!T && hasAssignableElements!(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~");"); }
  }

  const struct PutConf
  {
    bool newline = true, flush, exit;
    string floatFormat = "%.10f", delimiter = " ";
  }

  auto put(alias conf = "{}", T...)(T v)
  { mixin("const PutConf c = "~conf~"; putMain!c(v);"); }
  auto putB(alias conf = "{}", 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 putMain(PutConf c, T...)(T v)
    {
      foreach (i, w; v) {
        putOne!c(w);
        if (i < v.length-1) OUT.write(c.delimiter);
      }
      static if (c.newline) OUT.writeln;
      static if (c.flush) OUT.flush();
      static if (c.exit) exit(0);
    }
    auto putOne(PutConf c, T)(T v)
    {
      static if (isInputRange!T && !isSomeString!T) putRange!c(v);
      else if (isFloatingPoint!T) OUT.write(format(c.floatFormat, v));
      else OUT.write(v);
    }
    auto putRange(PutConf c, T)(T v)
    {
      auto w = v;
      while (!w.empty) {
        putOne!c(w.front); w.popFront();
        if (!w.empty) OUT.write(c.delimiter);
      }
    }
  }
}