def extract_calibration_value(line: str) -> int:
    # Find all digits in the current line.
    digits = [c for c in line if c.isdigit()]

    # If there are no digits, we skip the line. (Depending on input, you may choose to error out.)
    if not digits:
        return 0  # or raise an exception if appropriate

    # The calibration value is the concatenation of the first and last digit.
    calib_str = digits[0] + digits[-1]
    return int(calib_str)

def main():
    total = 0

    with open("input.txt", "r") as f:
        for line in f:
            # Remove potential newline or trailing spaces.
            line = line.strip()
            if not line:
                continue
            total += extract_calibration_value(line)

    print("Total calibration value:", total)

if __name__ == "__main__":
    main()

package main

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

func extractCalibrationValue(line string) int {
	var firstDigit, lastDigit rune
	foundFirst := false
	for _, char := range line {
		if unicode.IsDigit(char) {
			if !foundFirst {
				firstDigit = char
				foundFirst = true
			}
			lastDigit = char
		}
	}

	if !foundFirst {
		// No digit found in the line; returning 0.
		return 0
	}

	// Convert runes (digits) to their string equivalent.
	calibStr := string(firstDigit) + string(lastDigit)
	calibVal, err := strconv.Atoi(calibStr)
	if err != nil {
		// In case of conversion error; this shouldn't occur if the input is valid.
		log.Fatalf("Error converting %s to integer: %v", calibStr, err)
	}
	return calibVal
}

func main() {
	file, err := os.Open("input.txt")
	if err != nil {
		log.Fatalf("Failed to open input.txt: %v", err)
	}
	defer file.Close()

	total := 0
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		line := scanner.Text()
		if len(line) == 0 {
			continue
		}
		total += extractCalibrationValue(line)
	}
	if err := scanner.Err(); err != nil {
		log.Fatalf("Error reading input.txt: %v", err)
	}
	fmt.Println("Total calibration value:", total)
}