#include<bits/stdc++.h>
using namespace std;
long long n, m, x = 0;
int main()
{
	cin >> n;
	for(int i = 1;i <= n;i++)
	{
		cin >> m;
		x^=m;
	}
	cout << x;
	return 0;
}

#include<iostream>
#include<queue>
#include<stack>
#include<cmath>
#include<algorithm>
#include<cstring>
using namespace std; 
long long n[100000];
int main ()
{
    int a,b,c=0;//C要清零！！！！
	cin>>a;//输入不用教吧？啊？
    while(a--)
    {
		cin>>b;
        c^=b;//对其进行位运算操作
    }
//    int i=0;
//    while(n[i]%2!=1)
//    {
//    	i++;
//	}
	cout<<c;
    return 0;
}

不要抄哦！！！(0-0 )

#include<bits/stdc++.h>

using namespace std;
map<int,int> mp;
int n,x;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>x;
		mp[x]++;
	}
	for(auto x:mp){
		if(x.second%2!=0)cout<<x.first;
	}
	return 0;
  //this is so (two B),if you see,you
  //are (two B) too.
  //you shouldn't running this 程序 in
  //Dev.C++
}

```cpp
#include<bits/stdc++.h>
using namespace std;

int main(){
    int n;
    cin>>n;
    int x=0;
    for(int i=1;i<=n;i++){
        int s;
        cin>>s;
        x^=s;
    }
    cout<<x;
    return 0;
}

#include<queue>
#include<stack>
#include<cmath>
#include<algorithm>
#include<cstring>
using namespace std; 
int n[1000];
int main ()
{
    int a,b;
	cin>>a;
    while(a--)
    {
		cin>>b;
        n[b-1]++;
    }
    int i=0;
    while(1)
    {
    	if(n[i]%2==1)
    	{
    		cout<<i+1;
    		break;
		}
    	i++;
	}
    return 0;
}

不要抄哦（o-o )