What is the output of the following Java program (a single number)?

interface FunFun { int apply(int pre, int next); } public class QuizC { public static int reduceLeft(int[] arr, FunFun f) { int res = arr[0]; for (int i = 1; i < arr.length; i++) res = f.apply(res, arr[i]); return res; } public static void main(String[] args) { int[] num = { 1, 4, 6, 8 }; int a = reduceLeft(num, (p,n)->p+n); System.out.println(a); } }