I was tryping to solve problem https://codeforces.net/problemset/problem/617/E. I am using Mo's algorithm to solve this problem, but this giving me wrong ans on test case 7. Please help to find where did my code fail.

My Code // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

static bool cmp(vector<ll> &a , vector<ll> &b)
{
    if(a[0]/319 != b[0]/319) return a[0]/319 < b[0]/319;
    else return a[1] < b[1];
}

void ok(ll t)
{
    ll n , q , k;
    cin >> n >> q >> k;
    vector<ll> vt(n+1) , prefix(n+1 , 0);
    for(ll i = 1; i <= n; i++) cin >> vt[i];
    for(ll i = 1; i <= n; i++) prefix[i] = prefix[i-1]^vt[i];
    
    ll mp[1000500] = {0};
    vector<vector<ll>> query(q , vector<ll>(3));
    for(ll i = 0; i < q; i++) 
    {
        cin >> query[i][0] >> query[i][1];
        query[i][0]-=1;
        query[i][2] =i;
    }
    sort(query.begin(), query.end() , cmp);

    ll total = 0;
    vector<ll> ans(q , 0);
    ll left = 0 , right = -1;
    for(ll i = 0;i<q;i++)
    {
        // cout << query[i][0] << " " << query[i][1] << " " << query[i][2] << endl;
        while(left > query[i][0]) // add
        {
            left-=1;
            total += mp[k^prefix[left]];
            mp[prefix[left]]+=1;
        }
        while(right < query[i][1]) // add
        {
            right+=1;
            total += mp[k^prefix[right]];
            mp[prefix[right]]+=1;
        }
        while(left < query[i][0]) // remove
        {
            mp[prefix[left]]-=1;
            total -= mp[k^prefix[left]];
            left+=1;
        }
        while(right > query[i][1]) // remove
        {
            mp[prefix[right]]-=1;
            total -= mp[k^prefix[right]];
            right-=1;
        }
        ans[query[i][2]] = total;
    }

    for(ll i = 0;i<q;i++) cout << ans[i] << endl;
}

int main()
{
    // Shubham Kumar Jha
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

ifndef ONLINE_JUDGE
    freopen("zinput.txt", "r", stdin);
    freopen("zoutput.txt", "w", stdout);
endif

    ll t = 1;
    // cin >> t;
    for(ll i = 1;i<=t;i++)
    {
        ok(i);
    }
    return 0;
}