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

    for(int i=0; i<n-1; ++i)
        if (s[i]==s[i+1]) { cout<<"YES"<<endl; return 0; }

    for(int i=0; i<n-3; ++i)
        if (s[i]==s[i+2] and s[i+1]==s[i+3]) { cout<<"YES"<<endl; return 0; }

    cout<<"NO"<<endl;
}