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