Wormholes(ZCO120002) - Failing a test case

[dev_232]

Hey guys,
I am getting WA in one testcase in wormholes problem. Can anybody help?
problem link - ZCO12002 Problem - CodeChef
Submission link - CodeChef: Practical coding for everyone

[everule1]

    for(int i = 0 ; i < x; i++){
        cin >> go[i];
    }
    sort(go.begin(), go.end());
    for(ll i = 0 ; i < x; i++){
        cin >> back[i];
    }