// 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) {
    const set = new Set();

    A.forEach(num => {
        if(set.has(num)){
            set.delete(num);
        }else{
            set.add(num);
        }
    })
    
}

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

function solution(A) {
    const set = new Set();

    A.forEach(num => {
        if(set.has(num)){
            set.delete(num);
        }else{
            set.add(num);
        }
    })

    for(let num of set.values())
        retrun num;

}

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

function solution(A) {
    const set = new Set();

    A.forEach(num => {
        if(set.has(num)){
            set.delete(num);
        }else{
            set.add(num);
        }
    })

    for(let num of set.values())
        return num;

}

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

function solution(A) {
    const set = new Set();

    A.forEach(num => {
        if(set.has(num)){
            set.delete(num);
        }else{
            set.add(num);
        }
    })

    for(let num of set.values())
        return num;

}

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

function solution(A) {
    const set = new Set();

    A.forEach(num => {
        if(set.has(num)){
            set.delete(num);
        }else{
            set.add(num);
        }
    })

    for(let num of set.values())
        return num;

}