1 #include<stdio.h> 2 int main() 3 { 4 int n,x,m; 5 while(~scanf("%d",&n),n) 6 { 7 x=0; 8 while(n--) 9 { 10 scanf("%d",&m); 11 x^=m; 12 } 13 printf("%d\n",x); 14 } 15 return 0; 16 }