You are given a number NN. Find the sum of all numbers from 11 to NN.

### Input:

- First-line will contain the number NN.

### Output:

Print the answer in a single line.

### Constraints

- 1≤N≤1091≤N≤109

### Sample Input 1:

```
4
```

### Sample Output 1:

```
10
```

n=int(input())

abil=int((n*(n+1))/2)

print(abil)