A farmer wants to plant paddy crops in his farm. So he visited a near by agriculture shop to buy seeds. The shopkeeper showed the farmer various varieties of paddy seed. Each variety of paddy seed varies from one another especially on the **Number of Days D needed to water and it Growth Rate G.The quantity of water in certain units required by a single crop in a single day is same as the growth rate on that particular day.The Growth Rate G reduces by a value Reveryday which will reduce the water consumption by crops.The shopkeeper issued S number of seeds to the farmer and assuming all seeds will grow.write a program to find the units of Water Consumption W for D days.**

Input Format

The first line contains the value of Number of Seeds S, Growth Rate G, Number of Days D to grow and the Reduction in Growth Rate R

each separated by a space.

Output Format:

The first line contains the total units of Water Consumption W in D days.

Boundary Conditions:

1 <= S, G, D, R <= 999999

Example Input/Output 1:

Input:

10 5 5 1

Output:

150

Explanation:

The total number of seeds S the farmer will buy is 10

The number of days D the crop has to be watered is 5

The growth rate G of each seed is 5.

The growth rate G is reduced by R-value 1 on every day. So, for the day 1 G is 5, day 2 G is 4, day 3 it is 3 and so on.

The Water Consumption W for 5 days = 10*5 + 10*4 + 10*3 + 10*2 + 10*1 = 150 units

Example Input/Output 2:

Input:

100 10 10 0

Output:

10000

```
#include<stdio.h>
#include <stdlib.h>
int main()
{
long int s,g,d,r;
scanf("%li %li %li %li",&s,&g,&d,&r);
long int i,sum=0;
for(i=0;i<d;i++)
{
sum+=s*g;
g-=r;
}
printf("%li",sum);
}
```

```
#include <iostream>
using namespace std;
int main(int argc, char** argv)
{
long int seeds,growth,days,growth_red,water = 0;
cin >> seeds >> growth >> days >> growth_red;
for(int i=0;i<days;i++)
{
water += seeds*growth;
growth = growth - growth_red;
}
cout << water;
}
```

```
import java.util.*;
public class Hello {
public static void main(String[] args) {
Scanner s=new Scanner(System.in);
long se,g,d,r,w=0;
se=s.nextLong();
g=s.nextLong();
d=s.nextLong();
r=s.nextLong();
for(int i=1;i<=d;i++)
{
w+=se*g;
g-=r;
}
System.out.print(w);
}
}
```