func_code_string: #include <bits/stdc++.h>   using namespace std;   int main(int argc, char* argv[]) {     int v1, v2, t, d, sum, a, t1, t2;     while (cin >> v1 >> v2 >> t >> d) {       sum = v1 + v2;       for (int i = 2; i < t; i++) {         if (v1 <= v2) {           v1 += d;           sum += v1;         } else {           v2 += d;           sum += v2;         }       }       cout << sum << endl;     }     return 0;   }   