#include <stdio.h> int a[1000008]; int b[1000008]; int main(){ int n,found; scanf("%d",&n); //4 for(int i=1;i<=n;i++) scanf("%d",&a[i]); for(int i=1;i<=n ;i++) { if(a[i]==0) continue; found=0; for(int j=1;j<=n;j++) { if(i!=j && a[i]==a[j]) { a[i]=0; a[j]=0; found =1; break; } } if (found==0) { printf("%d",a[i]); break; } } return 0; } /* 9 1 1 9 11 5 3 11 5 9 */