C++ :

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <map>
#include <queue>
using namespace std;
#define out(v) cerr << #v << ": " << (v) << endl
#define SZ(v) ((int)(v).size())
const int maxint = -1u>>1;
template <class T> bool get_max(T& a, const T &b) {return b > a? a = b, 1: 0;}
template <class T> bool get_min(T& a, const T &b) {return b < a? a = b, 1: 0;}

const double pi = acos(-1.0);
const double eps = 1e-9;

int sgn(double x) {
    return (x > eps) - (x < -eps);
}

int n;


struct point {
    double x, y;
    point() {}
    point(double _x, double _y) : x(_x), y(_y) {}
};

double dis(double x, double y) {
    return sqrt(x * x + y * y);
}

vector<point> pts;
vector< pair<double, double> > vec;

bool check(const vector< pair<double, double> > &vec) {
    for(int i = 0; i < vec.size(); i++) {
        double len = vec[i].first;
        double arc = vec[i].second;
        for(int j = i + 1; j < vec.size(); j++) {
            if(sgn(vec[j].first - len)) {
                i = j - 1;
                break;
            }
            else {
                if(sgn(arc - vec[j].second) == 0 || sgn(fabs(arc - vec[j].second) - pi) == 0) {
                }
                else {
                    return true;
                }
            }
        }
    }
    return false;
}

bool getAnswer() {
    for(int i = 0; i < n; i++) {
        vec.clear();
        for(int j = 0; j < n; j++) {
            if(i == j) continue;
            double arc = atan2(pts[j].y - pts[i].y, pts[j].x - pts[i].x);
            double len = dis(pts[j].y - pts[i].y, pts[j].x - pts[i].x);
            if(sgn(arc) < 0) arc += 2 * pi;

            vec.push_back(make_pair(len, arc));
        }
        sort(vec.begin(), vec.end());
        if(check(vec)) return true;
    }
    return false;
}

int main() {
    //freopen("tri.in")
    //freopen("tri.out", "w", stdout);
    while(scanf("%d", &n) == 1) {
        pts.clear();
        for(int i = 0; i < n; i++) {
            double x, y;
            scanf("%lf%lf", &x, &y);
            pts.push_back(point(x, y));
        }
        printf(getAnswer() ? "YES\n": "NO\n");
    }
    return 0;
}