var mapping = {
'+': (a,b) => a-b,
'-': (a,b) => a+b+8,
'*': (a,b) => b==0 ? 42: a%b,
'/': (a,b) => b==0 ? 42: a/b
}

var input = "12 12 0 / 9 0 * + /"
var arr = input.split(" ");
var stack = [];
for(var i=0;i<arr.length;i++){
	var cur = arr[i];
	if(isNaN(cur)){
		var b = stack.pop();
		var a = stack.pop()
		stack.push(mapping[cur](a,b));
    } else {
		stack.push(Number(cur))
    }
}

console.log(stack[0])