def solve():
    n = int(input())
    a = list(map(int, input().split()))
    if n == 1:
        print("No")
        return
    if n == 2:
        if a[0] == a[1]:
            print("Yes")
        else:
            print("No")
        return
    for i in range(n-2):
        if a[i] == a[i+1] or a[i] == a[i+2] or a[i+1] == a[i+2]:
            print("Yes")
            break
    else:
        print("No")
solve()