#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000

string searchword[4] = { "00", "11", "0101", "1010" };

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int N; cin >> N;
	string S; cin >> S;
	rep(i, 4) {
		if (S.find(searchword[i]) != std::string::npos) {
			cout << "YES" << endl;
			return 0;
		}
	}
	cout << "NO" << endl;

    return 0;
}