#include <bits/stdc++.h>   using namespace std;   int64_t max(int32_t a, int64_t b) { return max((int64_t)a, b); }   int32_t main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     pair<int64_t, int64_t> lc, rc;     cin >> rc.second >> rc.first;     lc.first = lc.second = 1;     int64_t k;     cin >> k;     int64_t cnt = 0;     int64_t ans = 0;     int64_t cur = 1;     while (cnt < k) {       ans += (rc.first - lc.first + 1) * (rc.second - lc.second + 1);       rc.first--;       rc.second--;       lc.second++;       lc.first++;       ans -= (rc.first - lc.first + 1) * (rc.second - lc.second + 1);       cnt++;       rc.first--;       rc.second--;       lc.second++;       lc.first++;     }     cout << ans;   }   