const reverseCaptcha = str =>
	str.split('').reduce((sum, x, i, a) =>
		( x === a[i + 1] || (i === a.length - 1 && x === a[0]) ) ?
			sum + Number(x) :
			sum
	, 0)

// Demo input
let input = "12233545132218841"

reverseCaptcha(input) // -> 16