#define _USE_MATH_DEFINES
#include<iostream>
#include<vector>
#include<cstdio>
#include<string>
#include<algorithm>
#include <iomanip>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define all(a) (a).begin(),(a).end()

#define s(s,a,b) s.substr(a,b-a+1) 

typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;

int i, j, k;

int main()
{
    int N; string S;
    cin >> N >> S;
    REP(i, N)
    {
        j = i;
        while(2*j < N+1-i)
        {
            if (s(S,i,j) == s(S,j+1,j+(j-1-i)))
            {
                cout << "YES" << endl;
                return 0;
            }
            j++;
        }
    }
    cout << "NO" << endl;
    return 0;
}