Probability Through Experiments

const int MAXN = 41000;

int ipt[MAXN];

int main()
{
    LL n, r;
    int kase = 1;
    while (cin >> n >> r && (n && r))
    {
        REP(i, n)
        {
            int a, b;
            scanf("%d.%d", &a, &b);
            ipt[i] = a * 1000 + b;
        }
        sort(ipt, ipt + n);
        FF(i, n, n + n)
            ipt[i] = ipt[i - n] + 360000;
        LL ans = 0, idx, x;
        LL all = n * (n - 1) * (n - 2) / 6;
        REP(i, n)
        {
            idx = lower_bound(ipt + i, ipt + n + i, ipt[i] + 180000) - ipt;
            x = n + i - idx;
            if (x >= 2)
                ans += (x - 1) * x / 2;
        }
        cout << "Case " << kase++ << ": " << all - ans << endl;
    }
    return 0;
}