#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() {
    int n;
    cin >> n;
    string s;
    cin >> s;
    int flag = 0;
    if(n >= 4)flag = 1;
    if(flag == 0){
        rep(i,n-1)if(s[i] == s[i+1])flag = 1;
    }
    if(flag)yn;
    return 0;
}