#include<iostream>
#include<vector>
#include<set>
#include<map>
#include<list>
#include<stack>
#include<queue>
#include<bitset>
#include<array>
#include<algorithm>
#include<cstdio>
#include<string>
#include<cstdlib>
#include<numeric>
#define D long long
#define U unsigned
using namespace std;
D n, m,a, b, d, e, x, y, z;
D i, j, k;
char c,f;
string s;
D ans;
int main() {
    D t;
    cin >>a>>s;
    if (s == "010" || s == "101" || s == "01" || s == "10" || s == "0" || s == "1")
        cout << "NO" << endl;
    else
        cout << "YES" << endl;
}