#include <bits/stdc++.h>
using namespace std;
#define in(T,V) T V;cin>>V;

int main(){
    in(int,N);
    in(string,s);

    cout << ([&]()->bool{
        return 
            s.find("00")   != string::npos ||
            s.find("11")   != string::npos ||
            s.find("0101") != string::npos ||
            s.find("1010") != string::npos;
    }()?"YES":"NO") << endl;
}