#include <iostream>
#include <string>
using namespace std;
int main()
{
    int n;
    string s;
    cin>>n>>s;

    string res="NO";
    for(int i=0; i<n-1; ++i) if (s[i]==s[i+1]) res="YES";
    for(int i=0; i<n-3; ++i) if (s[i]==s[i+2] and s[i+1]==s[i+3]) res="YES";

    cout<<res<<endl;
}