while true:
        num = (num+ 1) % k;
        for (i = 0..len(a[num]))
            v = a[num];
            if (used[v])
                continue;
            used[v] = true
            for (u : m[v])
                if relax(v, u)
                    a[(num + e[v][u]) % k].push(u)