func_code_string: #include <bits/stdc++.h>   int main(int argc, const char* argv[]) {     int n;     std::cin >> n;     int step = 0;     int prev = 0;     int first = 0, second = 0;     bool prog = true;     int x = 0;     for (int i = 0; i < n; i++) {       std::cin >> x;       if (i == 0)         first = x;       else if (i == 1) {         second = x;         step = second - first;         prev = x;       } else {         if ((x - prev) != step) prog = false;         prev = x;       }     }     if (prog)       std::cout << x + step;     else       std::cout << x;     return 0;   }   