n = int(input())
a = list(map(int, input().split()))
dist = {}
idx = {}
for i in range(n):
    if a[i] not in idx:
        idx[a[i]] = i
    elif a[i] not in dist:
        dist[a[i]] = i - idx[a[i]]

for d in dist.values():
    if d <= 2:
        print("Yes")
        exit(0)
print("No")