func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int a, b, c, d;     while (~scanf( %d%d%d%d , &a, &b, &c, &d)) {       int t = d - c;       if (c - b == t && b - a == t) {         printf( %d n , d + t);       } else if (a != 0 && b != 0 && c != 0 && d != 0 && b * b == a * c &&                  c * c == b * d && d * d % c == 0) {         printf( %d n , d * d / c);       } else         printf( 42 n );     }     return 0;   }   