// you can also use imports, for example:
// import java.util.*;

// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

class Solution {
    public int solution(int[] A) {
        // write your code in Java SE 8
    }
}

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
}

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
  let arr = [];
  for (let i = 0; i < A.length; i++) {
    if (arr.indexOf(A[i]) === -1) {
      arr.push(A[i]);
    } else {
      arr = arr.filter((num) => num !== A[i]);
    }
  }
  return arr[0];
}

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
  let arr = [];
  for (let i = 0; i < A.length; i++) {
    if (arr.indexOf(A[i]) === -1) {
      arr.push(A[i]);
    } else {
      arr = arr.filter((num) => num !== A[i]);
    }
  }
  return arr[0];
}

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
  let arr = [];
  for (let i = 0; i < A.length; i++) {
    if (arr.indexOf(A[i]) === -1) {
      arr.push(A[i]);
    } else {
      arr = arr.filter((num) => num !== A[i]);
    }
  }
  return arr[0];
}