#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int>P;
typedef vector<int>VI;
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()

int N;
char str[1010101];

int main(){
    scanf("%d%s",&N,str);
    for(int i=0;i<N-1;i++){
        if(str[i]==str[i+1]){
            cout<<"YES"<<endl;
            return 0;
        }
    }
    
    if(N>=4)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}