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 pi units of goods. No more than si units of goods can be sold in the i-th city.

For each pair of cities i and j such that 1 \le i \lt j \le 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 andc (1 \le n \le 10000, 0 \le c \le 109)- the number of cities and the maximum amount of goods for a single transportation.

The second line contains n integers pi (0 \le pi \le 109)- the number of units of goods that were produced in each city.

The third line of input contains n integers si (0 \le si \le 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.