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The pretty little nenuphar

Statement

 Goal

Once upon a time, in a quiet and beautiful lake was a pretty little nenuphar.
But this pretty little nenuphar is expected to become HHUUUGGEEE !!!
The lake is a grid of dimensions WIDTH and HEIGHT.
The PLN (pretty little nenuphar) is at position X Y in the grid.
At day 0, the PLN occupy 1x1 cell.
Each day, the PLN occupies all surrounding cells.
So, at day 1, the PLN will occupy 9 (3x3) cells. At day 2, the PLN will occupy
25 (5x5) cells and so on.
But the PLN can only grow INTO THE LAKE obviously.
Which number of cells will the PLN occupy after N days ?
Input
3 lines containing 1 or 2 integers separated by spaces.
First line : WIDTH HEIGHT
Second line : X Y
Third line : N
Output
One line containing the number of cells occupied by the PLN after N days.
Constraints
1 <= WIDTH <= 1000000000
1 <= HEIGHT <= 1000000000
0 <= X < WIDTH
0 <= Y < HEIGHT
1 <= N <= 1000000000
Example
Input
10 10
4 4
1
Output
9

Game modes
Fastest

Test cases
After one day Test
Input
10 10 4 4 1
Output
9

After one day Validator
Input
10 10 4 4 1
Output
9

After two days Test
Input
10 10 4 4 2
Output
25

After two days Validator
Input
10 10 4 4 2
Output
25

After five days Test
Input
10 10 4 4 5
Output
100

After twelve days Validator
Input
50 50 28 5 12
Output
450

In a corner Test
Input
10 10 7 8 2
Output
20

1K Validator
Input
50 50 12 37 19
Output
1024

Another corner Test
Input
10 10 7 8 3
Output
30

A vertical lake Validator
Input
10 100 7 8 5
Output
88

Same corner but the day after Test
Input
10 10 7 8 4
Output
42

An horizontal lake Validator
Input
100 10 7 8 5
Output
77

What a f... huge lake !!! Test
Input
1000000000 1000000000 894150 24315138 580000000
Output
351043129605851989

What a f... huge lake !!! Validator
Input
1000000000 1000000000 795602854 699837200 500000000
Output
563632392655368800

Solution language

Solution

Stub generator input