450C - Jzzhu and Chocolate - CodeForces Solution

#include <bits/stdc++.h>
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define between(l, x, r) l <= x && x <= r
using namespace std;
using ll = long long;

void solve() {
  ll n, m, k;
  cin >> n >> m >> k;

  if (n > m) swap(n,m);

  if ((n-1)+(m-1) < k) {
    cout << -1 << endl;
    return;
  }

  if (n-1 >= k) {
    cout << max(m*(n/(k+1)), n*(m/(k+1))) << endl;
  }
  else if (n-1 < k && k <= m-1) {
    cout << n*(m / (k+1)) << endl;
  }
  else {
    cout << (n/(k+1-(m-1))) << endl;
  }

}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int t = 1;
  // cin >> t;
  while (t--) solve();
  #ifdef LOCAL_TIME
    cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "s\n";
  #endif
}