func_code_string: #include <bits/stdc++.h>   using namespace std;   void solve() {     long long w, h, k, ans = 0;     cin >> w >> h >> k;     for (long long i = h, j = w; i > 0, j > 0, k > 0; i -= 4, j -= 4) {       ans += 2 * i + 2 * j;       ans -= 4;       k--;     }     cout << ans << endl;   }   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     long double t = 1;     while (t--) {       solve();     }   }   