#include <stdio.h>
#include <iostream>
#include <algorithm>
#include<string>
#include <math.h>

using namespace std;




int main() {
	int a[7];
	int count = 0,p=1;
	cin >> a[0];
	for (int i = 1; i < 7; i++) {
		cin >> a[i];
		if (a[i - 1] == a[i])count++;
		if (count == 3) {
			cout << "NO" << endl;
			return 0;
		}
	}
		cout << "YES" << endl;
	return 0;
}