#include<iostream> //cin cout #include<cstring> #include<cstdio> //scanf printf using namespace std; int main(){ int k,c=1; char s[2500]; cin>>k>>s; for(int i=0;s[i]!='\0';i++){ if(c==k){ cout<<s[i]; return 0; } if(s[i]==s[i+1]) c++; else c=1; } cout<<"No"; return 0; }