#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))

#define MOD 1000000007

int main() {
    int n;
    cin>>n;
    string s;
    cin>>s;
    vector<string> v;
    v.pb("0");
    v.pb("1");
    v.pb("01");
    v.pb("10");
    v.pb("101");
    v.pb("010");
    if(count(all(v),s)==1){
      cout << "NO" << endl;
    }
    else{
      cout << "YES" << endl;
    }
    return 0;
}