#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:64000000")
const int infi = 1e9 + 7;
const long long infl = 1e18 + 7;
const long double eps = 1e-7;
const long double eps1 = 1e-6;
const int mod = (1e9 + 7);
const long long p1 = 29;
const long long p2 = 31;
const long long mod1 = 1e9 + 9;
const long long mod2 = 1e9 + 9;
const long long maxsz = 1000010;
int main() {
  int a, b, c;
  cin >> a >> b >> c;
  if (a > b) {
    swap(a, b);
  }
  if (b > c) {
    swap(b, c);
  }
  if (a > b) {
    swap(a, b);
  }
  int ans = 0;
  for (; b != 1; --b, --c, ++a) {
    ans += a;
  }
  ans *= 2;
  ans += a * c;
  cout << ans;
  return 0;
}
