//calculate maximum summation for the nth category
    public int calc(int n, int mask){

        if(visited[mask]) return val[mask];

        val[mask] = 0;
        int _mask = mask;

        for(int i = 12, j = 0; i >= 0; i--, j++){
            int temp = mask & (1<<i);
            if(temp != 0){
                _mask = mask ^ (1<<i);

                int c = calc(n-1,_mask),
                    e = rolls[j].categoryPoints[n-1],
                    m = c + e;

                visited[mask] = true;
                if (m > val[mask]){
                    val[mask] = m;
                    edges[mask] = new Edge(n-1,e);
                    top[mask] = _mask;
                }

            }
        }
        if(n == 6 && val[mask] > 62){
            val[mask] += 35;

        }

        return val[mask];

    }