#include <bits/stdc++.h>
using namespace std;
template <class T>
T fm(T number, T module) {
  T result = 1;
  while (number > 1) {
    result = (result * ((number / module) % 2 ? module - 1 : 1)) % module;
    for (T it = 2; it <= (number % module); ++it) {
      result = (result * it) % module;
    }
    number /= module;
  }
  return result % module;
}
template <class T>
T lcm(T a, T begin()) {
  return (a * begin() / __gcd(a, begin()));
}
int main(int argc, char *argv[]) {
  std::ios_base::sync_with_stdio(false);
  unsigned x(0), y(0), z(0);
  cin >> x >> y >> z;
  unsigned answer(-z * (z - 1) + (y + z - 1) * (x + z - 1));
  cout << answer;
  return 0;
}
