#include<iostream> #include<algorithm> #include<cstring> #include<bits/stdc++.h> using namespace std; int main(){ char a[2501]; int b=0,k; cin>>k; cin>>a; char c='a'; for(int i=0;a[i];i++){ if(a[i]==c){ b++; } else{ c=a[i]; b=1; } if(b==k){ cout<<c; break; } } if(b!=k){ cout<<"No"; } return 0; }