题解

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

int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);

int n;
cin >> n;
int r = 0;
int a;

for (int i = 0; i < n; i++) {
	cin >> a;
	r ^= a;  //0^a=a,a^a=0
    //r^2=2
    //2^2=0
    //0^1=1
    //1^3=01^11=10=2
    //2^3=10^11=01=1
    //1^3=01^11=10=2
    //2^2=0
    //0^3=3
    //3^1=11^01=10=2
    //r=2
}

cout << r << endl;
return 0;

}