Big Bang Secrets

Interview

Time limit2sMemory limit512 MB

Summary

Decode an uppercase word by shifting each letter backward by S = 3P + K positions, where P is the letter's 1-based position.

Level: Easy2 of 10
Topics: Implementation, String, Math
Solved: No attempts yet

Problem

Sheldon and Leonard are physicists obsessed with the BIG BANG theory. To exchange secret insights, they devised a code that encrypts UPPERCASE words by shifting each letter forward.

Shifting a letter by $S$ positions means moving forward $S$ letters in the alphabet. For example, shifting B by $S = 3$ positions gives E. Sometimes this moves past Z, the last letter of the alphabet; whenever that happens we wrap around, treating A as the letter that follows Z. For example, shifting Z by $S = 2$ positions gives B.

The code depends on a parameter $K$ and also varies with the position of each letter in the word. For the letter at position $P$ , the shift value used is $S = 3P + K$ . (The first letter is at position $P = 1$ .)

For example, here is how ZOOM is encoded when $K = 3$ . The first letter Z has shift value $S = 3 \times 1 + 3 = 6$ ; it wraps around and becomes F. The second letter O has $S = 3 \times 2 + 3 = 9$ and becomes X. The last two letters become A and B. So Sheldon sends Leonard the secret message FXAB.

Write a program for Leonard that decodes the messages Sheldon sends.

Input

The input consists of two lines. The first line contains the positive integer $K$ ( $K < 10$ ), used to compute the shift value. The second line contains the word: a sequence of uppercase letters of length at most 20.

Output

Output the decoded word of uppercase letters.

Examples2

Example 1
Input
```
5
JTUSUKG
```
Expected output
```
BIGBANG
```
Example 2
Input
```
3
FXAB
```
Expected output
```
ZOOM
```