Then after validation completes(when you submit correct output) then it will ask you to submit output file to original input file (will be provided) along with your source code and you'll have only ~5 min to submit it !

You can use this C++ snippet for Input Output files

#include<bits/stdc++.h>
using namespace std;

int main(){
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    
    // Your code goes here.

    return 0;
}