/* -*- coding: utf-8 -*-
 *
 * 3286.cc:  No.3286 Make a Happy Connection - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 500;

/* typedef */

/* global variables */

int as[MAX_N];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", as + i);

  bool ok = false;
  for (int i = 0; ! ok && i < n; i++)
    ok =
      (i + 1 < n && as[i] == as[i + 1]) ||
      (i + 2 < n && as[i] == as[i + 2]);
  
  if (ok) puts("Yes");
  else puts("No");

  return 0;
}