#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int a[101] = {0}; int main() { int n, x; cin >> n; for (int i = 1; i <= n; i++) { cin >> x; a[x]++; } for (int i = 1; i <= 100; i++) { if (a[i] == 1) { cout << i; } } return 0; }