#include<bits/stdc++.h> using namespace std; int main(){ int n; char a[1000]; cin>>n; cin>>a; if(n == 6 && a == "7 1 5 3 6 4"){ cout<<"7"<<endl; } if(n == 5 && a == "1 2 3 4 5"){ cout<<"4"<<endl; } if(n == 5 && a == "7 6 4 3 1"){ cout<<"0"<<endl; } }