Help me in solving CPPFALL161 problem

help
,
1

My issue

I don’t understand this prblm

My code

#include <iostream>
using namespace std;

int main()
{  int n;
  cin >> n
    string s;
    cin>>s; // input string
    cout<<s[n-1]<<s[n-4]<<s[n-6]<<"\n";
    
}

Learning course: Learn Programming and Problem Solving using C++
Problem Link: https://www.codechef.com/learn/course/sit-cpp-fall/SITFALL27/problems/CPPFALL161