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function hexToDecimal(hexString) {
  // Remove any leading '0x' if present
  if (hexString.startsWith('0x')) {
    hexString = hexString.slice(2);
  }
  
  // Convert the hex string to a decimal number
  const decimalNumber = parseInt(hexString, 16);
  
  // Check if the conversion is successful
  if (isNaN(decimalNumber)) {
    return 'Invalid hexadecimal number';
  }
  
  return decimalNumber;
}

function decimalToHex(decimalNumber) {
  // Check if the input is a valid number
  if (isNaN(decimalNumber)) {
    return 'Invalid decimal number';
  }
  // Convert the decimal number to a hexadecimal string
  const hexString = decimalNumber.toString(16).toUpperCase();
  return hexString;
}

var color = "FFFFFF"
console.log(color);
console.log(hexToDecimal(color))
console.log(hexToDecimal(color) - 10)
console.log(decimalToHex(hexToDecimal(color) - 10))