Affine Cipher

Jeongeun, trained in the western country, slipped into the eastern country. After getting hold of the eastern country's information, Jeongeun decided to use an affine cipher to send it back west safely.

An affine cipher is computed with this formula.

$E(X) = (aX + b) \bmod 26$

Map the letters A through Z to $0, 1, 2, \dots, 25$ in order. With $a = 3$ and $b = 1$, feeding the letter A into the formula gives $E(0) = (3 \times 0 + 1) \bmod 26 = 1$, so the encrypted result is B.

Given $a$, $b$, and a plaintext made only of uppercase letters, write a program that turns the plaintext into ciphertext.

The first line has the number of test cases $T$ ($1 \le T \le 50$).

The first line of each test case has two integers $a$ and $b$ ($0 < a, b \le 1\,000\,000$). $a$ is coprime with 26.

The second line of each test case has the plaintext $s$. Its length $|s|$ is greater than 0 and less than $1\,000\,000$, and $s$ consists only of uppercase letters.

For each test case, print the ciphertext of $s$ on its own line.