#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
//#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
//#include<list>
#include<queue>
#include<deque>
#include<algorithm>
//#include<numeric>
#include<utility>
#include<complex>
//#include<memory>
#include<functional>
#include<cassert>
#include<set>
#include<stack>

const int dx[] = {1, 0, -1, 0};
const int dy[] = {0, 1, 0, -1};
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    string s;
    cin >> s;
    if (N >= 4) {
        cout << "YES" << endl;
        return 0;
    }
    if (N == 1) {
        cout << "NO" << endl;
        return 0;
    }
    if (s == "01" || s == "10" || s == "010" || s == "101") {
        cout << "NO" << endl;
        return 0;
    }
    cout << "YES" << endl;
    return 0;
}