There are n cities located along the one-way road. Cities are numbered from 1 to n in the direction of the road.

The i-th city had produced p_i units of goods. No more than s_i units of goods can be sold in the i-th city.

For each pair of cities i and j such that 1 ≤ i < j ≤ n you can no more than once transport no more than c units of goods from the city i to the city j. Note that goods can only be transported from a city with a lesser index to the city with a larger index. You can transport goods between cities in any order.

Determine the maximum number of produced goods that can be sold in total in all the cities after a sequence of transportations.

The first line of the input contains two integers n and c (1 ≤ n ≤ 10 000, 0 ≤ c ≤ 10⁹) — the number of cities and the maximum amount of goods for a single transportation.

The second line contains n integers p_i (0 ≤ p_i ≤ 10⁹) — the number of units of goods that were produced in each city.

The third line of input contains n integers s_i (0 ≤ s_i ≤ 10⁹) — the number of units of goods that can be sold in each city.

Print the maximum total number of produced goods that can be sold in all cities after a sequence of transportations.