**Description**

Wangxiao boast a good knife, a large pancake was put on the chopping block, and asked him: "? Not allowed to leave the cake cutting board, cut n (1 <= n <= 100) can be divided into a maximum number of knife block"

**Input**

Enter the number of cutting knife n.

**Output**

Cutting n number of blocks knife up output is cut cake.

**Sample Input**

100

**Output**

5051

**Hint**

**This question in fact we have had this title in junior high school: a plane up to be "n" number of lines divided into blocks, is the same here, looking with "n" to increase the number of copies to be split What really changes : 2,4,7,11,16 ...... regularities good looking 2 + 2 + 4,4 = 7,7 = 3 + 4 + 5 = 16 = 11, 11 ...... recursive equation: a [n ] = n-1] + n +1 a [;**

```
#include <stdio.h>
#include <stdlib.h>
int main()
{
int n,i;
long long a[100]={0};
a[0] = 2;
scanf("%d",&n);
for(i=1;i<n;i++)
{
a[i] += a[i-1]+i+1;
}
printf("%lld\n",a[i-1]);
return 0;
}
```