#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;
using P = pair<int, int>;
constexpr ld EPS = 1e-12;
constexpr int INF = numeric_limits<int>::max() / 2;
constexpr int MOD = 1e9 + 7;

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    string s;
    cin >> n >> s;
    if (n == 1)
    {
        cout << "NO" << endl;
    }
    else if (n == 2)
    {
        if (s[0] == s[1])
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
    else if (n == 3)
    {
        if (s == "010" || s == "101")
            cout << "NO" << endl;
        else
            cout << "YES" << endl;
    }
    else
        cout << "YES" << endl;
}