///////////////////////     COMMON    //////////////////////
#include <bits/stdc++.h>
using namespace std;
#define fio                           \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);
#define sb(n) __builtin_popcount(n)
#define endl '\n'
#define ll long long
#define ul unsigned long long
#define dl double
#define pub push_back
#define pob pop_back
#define len(a) (int)a.size()
#define fi first
#define se second
#define mpf(mp, k) mp.find(k) != mp.end()
#define mpnf(mp, k) mp.find(k) == mp.end()
#define lb(arr, tar) lower_bound(arr.begin(), arr.end(), tar) - arr.begin()
#define ub(arr, tar) upper_bound(arr.begin(), arr.end(), tar) - arr.begin()
#define pr(x, y) pair<x, y>
#define prdl(n) cout << fixed << setprecision(n)
#define ff(i, a, b, inc) for (int i = a; i <= b; i += inc)
#define fb(i, a, b, inc) for (int i = a; i >= b; i -= inc)
///////////////////////     WORLD    //////////////////////
ll mod = 998244353;

template <typename T, typename... Args>
auto V(size_t n, Args... args)
{
    if constexpr (sizeof...(args) == 1)
        return vector<T>(n, args...);
    else
        return vector<decltype(V<T>(args...))>(n, V<T>(args...));
}

///////////////////////     OUTPUTS    //////////////////////
template <typename... T>
void print(T... args)
{
    ((cout << args << " "), ...);
    cout << endl;
}

template <typename T>
struct is_vector : std::false_type
{
};

template <typename T, typename Alloc>
struct is_vector<std::vector<T, Alloc>> : std::true_type
{
};

template <typename T>
void printV(const T &val)
{
    std::cout << val;
}

template <typename T>
void printV(const vector<T> &v)
{
    for (size_t i = 0; i < v.size(); ++i)
    {
        printV(v[i]);
        if constexpr (!is_vector<T>::value)
        {
            if (i < v.size() - 1)
                cout << " ";
        }
    }
    if constexpr (!is_vector<T>::value)
    {
        cout << '\n';
    }
}

void printG(auto &G)
{
    int node = 0;
    for (auto &it : G)
    {
        cout << node++ << " -> ";
        printV(it);
        cout << endl;
    }
}

void printM(auto &M)
{
    for (auto &it : M)
        cout << it.fi << " -> " << it.se << endl;
}

////////////////////////////    main   ///////////////////////

void solve()
{
    int n;
    cin >> n;
    unordered_map<int, int> Mp;
    ff(i, 0, n - 1, 1)
    {
        int a;
        cin >> a;
        if (Mp.find(a) != Mp.end() && i - Mp[a] <= 2)
        {
            print("Yes");
            return;
        }
        Mp[a] = i;
    }
    print("No");
}

int main()
{
    fio;
    prdl(10);
    solve();
    return 0;
}