func_code_string: #include <bits/stdc++.h>   using namespace std;   const int mx = 8e3;   void run_case(void) {     int n;     cin >> n;     vector<int> x(n);     for (int i = 0; i < n; i++) cin >> x[i];     int d = x[1] - x[0];     for (int i = 1; i < n - 1; i++) {       if (x[i + 1] - x[i] != d) {         cout << x[n - 1] << endl;         return;       }     }     cout << x[n - 1] + d << endl;   }   int main(void) {     ios_base ::sync_with_stdio(false);     cin.tie(NULL);     run_case();     return 0;   }   