#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int s1=1,k; char s[1001]; cin>>k>>s; for(int i=0;s[i]!='\0';++i){ if(s1==k){ cout<<s[i]; return 0; } else { if(s[i]==s[i+1]) s1++; else s1=1; } }cout<<"No"; return 0; }