The sequence number is calculated using the formula:
$f(n) = (a^b + c^d) \mod 10$
**Task**: Given four positive integers $a$, $b$, $c$, and $d$ $(1 \leq a, b, c, d \leq 10^9)$, find the last digit of $f(n)$.
#### Input
- The first line contains a positive integer $T$ $(1 \leq T \leq 10^5)$, which is the number of data sets.
- The following $T$ lines each contain four positive integers $a$, $b$, $c$, and $d$.
#### Output
- Print $T$ lines, each containing a single digit, which is the last digit of $f(n)$ for the corresponding input data set.
#### Example
Input:
```
2
1 1 1 3
1 1 3 3
```
Output:
```
4
2
```
#### Subtasks
- **Subtask 1 (40 points)**: $a, b, c, d \leq 10^3$.
- **Subtask 2 (30 points)**: $a, b, c, d \leq 10^5$.
- **Subtask 3 (30 points)**: No additional constraints.
