```go
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)

	if !scanner.Scan() {
		return
	}
	n, _ := strconv.Atoi(scanner.Text())

	if !scanner.Scan() {
		return
	}
	pVal, _ := strconv.Atoi(scanner.Text())
	p := int64(pVal)

	a := make([]int64, n)
	var totalSum int64
	for i := 0; i < n; i++ {
		scanner.Scan()
		val, _ := strconv.ParseInt(scanner.Text(), 10, 64)
		a[i] = val
		totalSum += val
	}

	var maxScore int64 = 0
	var currentSum int64 = 0

	// We iterate through all possible split points.
	// A split point i means the first part is a[0]...a[i]
	// and the second part is a[i+1]...a[n-1].
	// i ranges from 0 to n-2 to ensure both parts have at least one element.
	for i := 0; i < n-1; i++ {
		currentSum += a[i]
		
		part1Score := currentSum % p
		part2Score := (totalSum - currentSum) % p
		
		totalScore := part1Score + part2Score
		if totalScore > maxScore {
			maxScore = totalScore
		}
	}

	fmt.Println(maxScore)
}
```