from itertools import pairwise

N = int(input())
A = list(map(int, input().split()))


def solve():
    for a, b in pairwise(A):
        if a == b:
            return True

    for i in range(N):
        if i+2 < N and A[i] == A[i+2]:
            return True

        if i > 0 and A[i-1] == A[i]:
            return True

    return False


ans = solve()
if ans:
    print('Yes')
else:
    print('No')