#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>

#define REP(i,n) for(long (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(long (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(long (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(long (i)=(a)-1;(i)>=(b);(i)--)
#define MOD 1000000007
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define VI vector<int>
#define VL vector<long>
#define VD vector<double>
#define PII pair<int,int>
#define PDD pair<double,double>
#define PLL pair<long,long>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define RSORT(a) sort((a).begin(),(a).end(),greater<int>())
#define MP(a,b) make_pair(a,b)
#define FORE(a,b) for(auto &&a:b)

typedef long long LL;
typedef unsigned long long ULL;

using namespace std;

int main(void){
    int N; cin>>N;
    string s; cin>>s;
    REP(i,N){
        FOR(j,i,N){
            if(j+1-i>=N) continue;
            if(s.substr(i,j-i)==s.substr(j+1,j+(j+1-i)-(j+1))){
                cout<<"YES"<<endl; return 0;
            }
        }
    }
    cout<<"NO"<<endl;
}