#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int N;
string S;
const string YES = "YES", NO = "NO";

string solve(){
    if(S.find("11") != string::npos)return YES;
    if(S.find("00") != string::npos)return YES;
    if(sz(S) > 3)return YES;
    return NO;
}

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    while(cin >> N >> S){
        cout << solve() << endl;
    }
}