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E. Goods transportation

time limit per test

2 secondsmemory limit per test

256 megabytesinput

standard inputoutput

standard outputThere 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.

Input

The first line of the input contains two integers *n* and *c* (1 ≤ *n* ≤ 10 000, 0 ≤ *c* ≤ 10^{9}) — 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} ≤ 10^{9}) — 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} ≤ 10^{9}) — the number of units of goods that can be sold in each city.

Output

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

Examples

Input

3 0

1 2 3

3 2 1

Output

4

Input

5 1

7 4 2 1 0

1 2 3 4 5

Output

12

Input

4 3

13 10 7 4

4 7 10 13

Output

34

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