# include<iostream> # include<cstring> # include<cstdio> using namespace std; int main(){ int k; cin>>k; char a[2500]; cin>>a; int s=1; for(int i=0;i<strlen(a);i++){ if(s==k){ cout<<a[i]<<endl; return 0; } if(a[i]==a[i+1]) s++; else s=1; }cout<<"NO"<<endl; return 0; }