// #pragma GCC optimize ("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target ("avx,avx2,fma")
#include <bits/stdc++.h>

using std::cin, std::cout, std::cerr;
using ll = long long;

int main() {
    std::ios::sync_with_stdio(false);
    int n;
    std::string s;
    cin >> n >> s;
    if(s == "1" || s == "0" || s == "10" || s == "01" || s == "101" || s == "010")
        cout << "NO\n";
    else
        cout << "YES\n";
}