#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <deque>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

#define p(s) cout<<(s)<<endl
#define REP(i,n,N) for(int i=n;i<N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=n;i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define F first
#define S second
typedef long long int ll;
using namespace std;
const int mod=1e9+7;

int N;
string s;
int main(){
    cin>>N>>s;
    if(N>=4) p("YES");
    else if(N==1) p("NO");
    else{
        bool f=false;
        REP(i,0,s.size()-1){
            if(s[i]==s[i+1]){
                f=true;
            }
        }
        p(f?"YES":"NO");
    }
    return 0;
}