import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

import java.util.ArrayList;

import java.util.List;

 

 

public class Main {

private static String str;

 

 

public static void main(String[] args) throws IOException {

BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

while ((str = reader.readLine()) != null) {

String[] tmp = str.split(" ");

int numPoints = Integer.parseInt(tmp[0]);

int numLines = Integer.parseInt(tmp[1]);

List<Point> points = new ArrayList<Point>();

for (int i = 0; i < numLines; i++) {

String tmp2[] = reader.readLine().split(" ");

int x = Integer.parseInt(tmp2[0]);

int y = Integer.parseInt(tmp2[1]);

points.add(new Point(x, y));

points.add(new Point(y, x));

}

boolean correct = false;

boolean keepLoop = true;

for (int i = 0; i < points.size(); i++) {

Point point = points.get(i);

point.connections++;

for (int j = i; j < points.size(); j++) {

Point point2 = points.get(j);

if (point2.number == point.number && point2.connectedWith != point.connectedWith) {

point.connections += 1;

if (point.connections == 4) {

correct = true;

keepLoop = false;

break;

}

}

}

if (!keepLoop) break;

}

 

if (correct) {

System.out.println("YES");

} else {

System.out.println("NO");

}

}

}

 

static class Point {

int number = 0;

int connectedWith = 0;

int connections = 0;

 

public Point(int number, int connectedWith) {

this.number = number;

this.connectedWith = connectedWith;

}

 

void setConnections(int connections) {

this.connections = connections;

}

 

int getConnections() {

return this.connections;

}

}