#include <iostream> #include <cstdio> using namespace std; int main() { int n,t=0,h=0; cin>>n; int a[n]; for (int i=0;i<n;i++){ cin>>a[i]; t+=a[i]; } for (int i=0;i<(n+1)/2;i++){ h=(i*2-1)*2+h; } cout<<h-t; return 0; }