function solve (alienNumber, sourceLanguage, targetLanguage) {
	decToAlien (alienToDec (alienNumber, sourceLanguage), targetLanguage);
}

function alienToDec (alienNumber, sourceLanguage) {
		var i,
		num = 0;

	alienNumber = alienNumber.split("").reverse().join("");
	for (i = 0; i < alienNumber.length; i++) {
		num += Math.pow(sourceLanguage.length, i) * sourceLanguage.indexOf(alienNumber[i]);
	}

	return num;
}

function decToAlien (num, targetLanguage) {
	//TODO
}

console.log(solve('13', '0123456789abcdef', '01'));
console.log(solve('Foo', 'oF8', '0123456789'));
console.log(solve('9', '0123456789', 'oF8'));